Rinexmod

- shell programs are now in a `bin` folder and are set as executable in the `setup.py`
- **the frontend command line interface program has been renamed `rinexmod_run.py` to avoid conflict with the module name**
- add `shortname` option to force RINEX file renaming with short name convention, and modify `longname` option to force RINEX file renaming with long name convention
(Behavior of previous `longname` option was ambiguous.)
`shortname` is mutually exclusive with `longname`.

* `--tolerant_file_period/-tol` is replaced by a more flexible --filename_style/-fns option.
* it takes now one string argument with 3 acceptable values: 'basic' (per default), 'flex', and 'exact'.
see help for more details
* misc. improvements and bug corrections

Misc improvements:

* Enhanced log messages
* Some exception handling when reading RINEX
* RINEX version attribute is now also float
* you can now remove your input RINEXs with -rm, but be carful of what you are doing!

make rinexmod compliant with IGSMAIL-8458, i.e. nine characters site in sitelogs, and Country or Region field instead of Country.

- **important user interface change**
- The arguments ``RINEXINPUT`` and ``OUTPUTFOLDER`` are now positional and require options ``-i/--rinexinput`` and ``-o/--outputfolder``, i.e.:
- ``-i RINEXINPUT [RINEXINPUT ...], --rinexinput RINEXINPUT [RINEXINPUT ...]``
- ``-o OUTPUTFOLDER, --outputfolder OUTPUTFOLDER``
- previous ``-i`` and ``-o`` are now:
- ``-ig, --ignore``
- ``-ol OUTPUT_LOGS, --output_logs OUTPUT_LOGS``
- import of GAMIT's files _station.info_ & _apr/L-file_ is now possible with `-sti` and `-lfi` options
- Refactoring: `SiteLog` class becomes `MetaData` class for more versatility. Many functions and variables have been renamed accordingly.
- add an option `-nh/--no_hatanaka` and `-co/--country`
- Misc. bugs correction

_Under the hood_ improvements:
- add the `rinexmod` module (folder)
- add `setup.py` for assisted installation

:warning: inform the developer if you meet import troubles

NB: present v2.2.1 corrects an import bug for front-end programs