Header format support

[tk3369]

This PR adds support for the "Header" format.

• Here is the official spec of the format
• I started following the Python implementation but then refactored to cleaner code
• I added @debug to a bunch of functions. I hope that's OK but we can remove some of them if it's deemed too excessive.
• The existing clnt.jl & srvr.jl test script has been updated to use Header format. (It would be nice to rework the test to cover more combinations by default but that should be a separate PR.)
• A new test script has been added: test/headertransport_tests.jl

P.S. I haven't cleaned up my commits. It's probably better to just squash everything when this PR is merged.

[codecov-commenter]

Codecov Report

Merging #70 (3e236cb) into master (1f2f5ab) will increase coverage by 6.11%. The diff coverage is 83.49%.

@@            Coverage Diff             @@
##           master      #70      +/-   ##
==========================================
+ Coverage   58.30%   64.42%   +6.11%     
==========================================
  Files           8        9       +1     
  Lines         969     1276     +307     
==========================================
+ Hits          565      822     +257     
- Misses        404      454      +50     

Impacted Files	Coverage Δ
src/Thrift.jl	100.00% <ø> (ø)
src/server.jl	62.85% <0.00%> (-1.85%)	:arrow_down:
src/protocols.jl	62.75% <70.73%> (+1.08%)	:arrow_up:
src/utils.jl	73.68% <73.68%> (ø)
src/transports.jl	71.18% <86.95%> (+36.00%)	:arrow_up:

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[tk3369]

I wasn't sure why CI failed on Julia 1.3, and I wasn't able to reproduce the issue on my local desktop with Julia 1.3. Checking the code, the InfoIDEnum value should be constructed only when the value is non-zero but the test failure clearly said that it's zero. So My guess is that the if-condition may be too strict. The latest commit made it use == rather ===.

[tanmaykm]

Thanks!