Support for CRAM beta coding

[athos]

This PR adds support for CRAM beta coding.

For more information on beta coding, see the CRAM specification.

The core of this PR is the BitStreamDecoder, which is a bit stream decoder. The BitStreamDecoder manages two states buffer (the byte value already read) and nbits (indicating how many bits of the buffer are still "alive") and prepares for reading the next bit sequence.

The CRAM reader creates a BitStreamDecoder based on the core block (the only bit-encoded data block) and shares it between data series that are declared to be beta-encoded (Although the CRAM specification does not explicitly state that a core block may be associated with multiple data series, it seems to be guaranteed by the fact that a test file (1101_BETA.cram) provided by hts-specs is encoded as such).

[codecov]

Codecov Report

Attention: Patch coverage is 94.11765% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 88.49%. Comparing base (1dd64cd) to head (e00b3fa).

Files	Patch %	Lines
src/cljam/io/cram/bit_stream.clj	88.88%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #309      +/-   ##
==========================================
+ Coverage   88.48%   88.49%   +0.01%     
==========================================
  Files          94       95       +1     
  Lines        8148     8173      +25     
  Branches      505      506       +1     
==========================================
+ Hits         7210     7233      +23     
- Misses        433      434       +1     
- Partials      505      506       +1     

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[alumi]

Thank you for adding this feature!
I checked both implementation and tests.
LGTM 👍 👍

[r6eve]

LGTM! Thank you for the PR.