Sportsreference

**Fixes**
* Fixed an issue where an error was thrown in the `Boxscores` classes for any game that doesn't have a score associated with it, such as games in the future or games that occur on the current day but haven't been updated yet.
* Added missing parameters to the NCAA `Boxscores` classes to indicate the names and abbreviations of both the winners and losers, if applicable.

**Enhancements**
* Expanded the amount of metrics of the `Boxscores` classes by including additional properties such as the final score, plus the names and abbreviations of both the winners and losers. For NCAAB and NCAAF, team rankings are also included when applicable, as well as a Boolean value to indicate whether the game includes at least one Top 25 team.
* The `Boxscores` class for all sports can now be iterated over a range with one call instead of just returning a single day's or week's worth of games. This new method is both easier to use and more performant by reducing the number of times the `Boxscores` class needs to be instantiated to get multiple dates.

**Fixes**
* Fixed an issue with the NFL documentation where an example on using the `Boxscores` class used invalid parameters which would throw an error when used in practice. The example has been updated with the correct parameters for calling the NFL `Boxscores` class.

**Known Issues**
* An error is thrown when pulling boxscores that don't have a score associated with it yet. The error is only thrown for all future boxscores as well as any games that occur on the current day. To avoid this issue, either avoid querying future boxscores or upgrade to a newer version of `sportsreference`.

**Fixes**:
* Fixed an issue where NCAAB rankings always returned an empty dictionary

**Enhancements**
* Improved the repository's community accessibility and availability by adding the following:
* A Code of Conduct that everyone who interacts with this repository is required to follow
* Pull Request, Issue, and Feature Request templates
* A Contributing file which provides guidelines that all contributors should follow when creating updates
* Updated code style checker from `PEP8` to `pycodestyle`

**Fixes**
* Fixed an issue parsing boxscore information for older games where less details are displayed, causing incorrect or mismatching information to be saved in various game information in the `Boxscore` class.
* Updated escape sequences for regex statements to enable the highest compatibility with future Python releases.
* Added specificity to all error handlers to ensure the code will provide meaningful information, or throw an error whenever an unexpected issue occurs.

**Enhancements**
* Added the `Player` class for all sports which allows individual players to be queried for season and career stats.
* Added the `Roster` class which instantiates a `Player` for every member of a team's roster to allow entire teams to be searched.
* Added a `Rankings` class for NCAAB and NCAAF which provides weekly rankings from the Associated Press.
* Added a `Conferences` class for NCAAB and NCAAF which contains the name of the conference each college team participates in.
* Now calculating more stats in the NCAAB `Team` class to provide more parity with the `Boxscore` class.
* Added a property in the `Game` class with the boxscore's URI to allow all URI's to be pulled without instantiating the `Boxscore` class.
* Re-arranged the layout of the docs to enable easier navigation.

**Fixes**
* Fixed spelling issues in documentation.
* Fixed an issue where an error was thrown while parsing the NHL boxscore meta-information when no information is provided.
* Fixed an issue parsing an NCAAB team's ranking in the `Boxscore` class when the boxscores aren't present on the requested boxscore page.

**Known Issues**
* For more historic seasons (generally 5+ years ago), the boxscore pages contains less game meta-information (such as date, location, attendance, etc.) which causes the incorrect values to be parsed. This does not affect the statistical values (points, shots, fouls, yards, hits, etc.) for the boxscores. Until fixed, it is recommended to not rely on the game meta-information for seasons prior to the most recent for all sports.

**Enhancements**
* Now using a universal PIP wheel instead of wheels specific to Python2 and Python3 as both use the same codebase.

**Fixes**
* Added error handling to all properties to prevent errors when incomplete/missing/invalid data is present on sports-reference.com.
* Replaced default value of all invalid properties with `None` to allow missing data to be distinguished from valid data where the result is zero (ie. A team that scored `0` touchdowns vs. a team that didn't have the number of touchdowns recorded).
* Fixed an issue where the `dataframe_extended` property would throw an error when no boxscores were created for a given year (seasons prior to 2010-2011 for NCAAB for example).
* Fixed an issue where NCAAB team records wouldn't be parsed when the advanced stats table wasn't included with the boxscore.
* Fixed an issue where missing NHL game meta-information on a boxscore would throw an error.

**Known Issues**
* For more historic seasons (generally 5+ years ago), the boxscore pages contains less game meta-information (such as date, location, attendance, etc.) which causes the incorrect values to be parsed. This does not affect the statistical values (points, shots, fouls, yards, hits, etc.) for the boxscores. Until fixed, it is recommended to not rely on the game meta-information for seasons prior to the most recent for all sports.