Handling entry types with capitalised letters

[kaustubhmote]

This PR fixes #70. Briefly, the comment and preamble types were previously recognised only if the @comment or @preamble was denoted by lowercase letters. This made bib files generated by other libraries that use capitalised letters (for example @Comment) incompatible with bibo. The comparison is now done with the variable type_ converted to lowercase.

This PR does not change the default behaviour of bibo.

[codecov[bot]]

Codecov Report

Merging #72 into dev will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev      #72   +/-   ##
=======================================
  Coverage   98.54%   98.54%           
=======================================
  Files          21       21           
  Lines        1168     1168           
=======================================
  Hits         1151     1151           
  Misses         17       17           

Impacted Files	Coverage Δ
bibo/internals.py	93.83% <100.00%> (ø)
pybibs/_internals.py	100.00% <100.00%> (ø)
pybibs/pybibs.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 40ce657...d032e84. Read the comment docs.

[Nagasaki45]

Thanks @kaustubhmote! What do you think about treating string types the same way? It seems to me that all checks on types should be case insensitive.

[kaustubhmote]

You are right, string type should also be checked. I pushed another commit in this branch to do this. I tried to look for other places in the code base where this may be required, but seems like this covers all the places where this is required. Let me know if there is someplace that I missed

Also, the base branch for this PR is now dev as well.

[Nagasaki45]

Amazing! BTW, feel free to send a PR adding you to the contributors file :-)