Add support for removing fixed-length headers from interpreted messages

[MattPrit]

Fixes #78

[DominicOram]

I believe failing tests are due to tholo/pytest-flake8#87 and unrelated to this PR

[codecov]

Codecov Report

Merging #80 (da5451b) into master (eac7366) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #80   +/-   ##
=======================================
  Coverage   98.56%   98.56%           
=======================================
  Files          65       67    +2     
  Lines        2085     2097   +12     
=======================================
+ Hits         2055     2067   +12     
  Misses         30       30           

Impacted Files	Coverage Δ
tickit/adapters/interpreters/wrappers/__init__.py	100.00% <100.00%> (ø)
...ers/interpreters/wrappers/beheading_interpreter.py	100.00% <100.00%> (ø)

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[garryod]

Looks really good! I'm a fan of the idea of composing interpreters. my only real questions (detailed below) are around the location in the package and use as a decorator

[garryod]

Lgtm

[DominicOram]

Generally looks good to me (as we pair programmed some of it) but could you add some user docs to https://github.com/dls-controls/tickit/blob/master/docs/tutorials/creating-an-adapter.rst?

[DominicOram]

Do expedite merging I have pulled documentation into #87