Nistbeacon

- Badges made to point to their release branches

- General
- Lots of documentation added through `docstrings`! :memo:
- `NistRandomnessBeacon`
- The beacon now understands how to check the chain. Using the `chain_check`
method on the beacon with a given `timestamp` value the NIST Randomness
Beacon chain can be verified for integrity purposes. :link:

python
classmethod
def chain_check(cls, timestamp: int) -> bool:
"""
Given a record timestamp, verify the chain integrity.

:param timestamp: UNIX time / POSIX time / Epoch time
:return: 'True' if the timestamp fits the chain. 'False' otherwise.
"""


- `NistRandomnessBeaconValue`
- :warning: All properties of the beacon have been placed behind `property`
decorators to minimize possible manipulation
- :warning: `verify_signature` has been removed from beacon values.
**Replaced with `valid_signature`**
- Introduced `valid_signature` as a `bool` property.
**Replaces `verify_signature`**

- Added a `verify_signature` to `NistRandomnessBeaconValue` objects.
This method returns a `True` or `False` after verifying the provided
record. The record is verified using two steps:
- First, using a combination of input data of the record, a simple message
is packed to create a message. That message is then used in combination with
the record's reported `signature_value` and the **known**
[NIST Beacon X.509 certificate](https://beacon.nist.gov/certificate/beacon.cer).
This certificate is available for download, but is baked into the application
as follows:
- Original CER file as a string: `nist_beacon_constants.py - NIST_CER_FILE`
- Original Public Key as a string: `nist_beacon_constants.py - NIST_RSA_KEY`
- Hard copy of `beacon.cer` is provided at the root of the project
- Second, the `signature_value` is ran through a `sha512` hash to confirm the
`output_value` is correct on the record.
- If either of the steps are found to be invalid, `verify_signature` will
return a `False` result.

- Added `to_xml`, `to_json`, and `from_json` methods on beacon values

- Initial PyPI release package