document COV_EXCL_START, COV_EXCL_STOP and COV_EXCL_LINE

[t-bltg]

Fix #326.

@IainNZ, @fingolfin or @kshyatt, bump ?

[coveralls]

Pull Request Test Coverage Report for Build 3404183565

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.1%) to 91.111%

---

Files with Coverage Reduction	New Missed Lines	%
src/coveralls.jl	2	94.74%
src/codecovio.jl	3	87.39%

Totals
Change from base Build 2585549201:	0.1%
Covered Lines:	205
Relevant Lines:	225

---

💛 - Coveralls

[codecov]

Codecov Report

Merging #335 (94ae19a) into master (1bc2ab4) will increase coverage by 0.44%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #335      +/-   ##
==========================================
+ Coverage   90.66%   91.11%   +0.44%     
==========================================
  Files           2        2              
  Lines         225      225              
==========================================
+ Hits          204      205       +1     
+ Misses         21       20       -1     

Impacted Files	Coverage Δ
src/coveralls.jl	94.73% <0.00%> (-1.76%)	⬇️
src/codecovio.jl	87.38% <0.00%> (+2.70%)	⬆️

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[kshyatt]

LGTM. Any barrier to merging this?

[vtjnash]

Maybe should be over on CoverageTools.jl, since this is not a feature here anymore?