Nistbeacon

- Project Changes
- Switched to `pycryptodome` from `pycrypto`.
- Started locking versions for `requirements.txt`.
- Created a `sphinx` based documentation site.
- Internal Changes
- Synced `LICENSE` file to use boilerplate notice.
- Removed `nist_records` dependency on `NistBeaconValue`
- Removed `local_record_db`. Most records are stored in `json` now.

- Updated `LICENSE` to work with GitHub LICENSE features.
- Updated `README` links for Codecov,
- Fixed `CONTRIBUTING` link in `README`.
- Updated library to use additional signing key
- For more details, see:
- https://github.com/urda/nistbeacon/issues/22
- https://github.com/urda/nistbeacon/issues/26

- Internal Changes
- LICENSE
- Updated for 2016.
- `NistBeacon`
- `get_first_record` now defaults to downloading the first record.
- `NistBeaconCrypto`
- Now computes the `struct` and other values for the `SHA512Hash`.
- `NistBeaconValue`
- Pushed `struct` and signature hash building into
`NistBeaconCrypto`.
- Project Changes
- Coverage Tool
- Switched from Coveralls to Codecov.

- Internal Changes
- `NistBeacon`
- `NIST_BASE_URL` renamed to `_NIST_API_URL`, to clarify that the value
should **NOT** be altered under normal circumstances.
- `NistBeaconCrypto`
- New helper class for signature checking of `NistBeaconValue` objects.
This is **NOT** a class designed for general use!
- `NistBeaconValue`
- Added a helper class `NistBeaconCrypto` to handle SHA512 generation
and signature checking. This means that `NistBeaconCrypto` needs to
be the only reference for key import and signature checking. All
other `NistBeaconValue` do not have to generate the full RSA objects.
- Started using the now existing `xmlns` property directly from NIST.

- Features
- `NistBeaconValue`
- Added a `pseudo_random` property.
Returns a `random.Random` object that has been seeded with
the `output_value` for a given `NistBeaconValue`.

- Internal Changes
- `NistBeaconValue`
- Creating a beacon value will store the JSON, XML representations once.
These values do not have to be computed on each `json` or `xml` property
access now as before.
- Project Changes (for Developers)
- `pylint` has been added to the project and build process.