Add a method of git() that bypasses cmd parsing.

[GunnarFarneback]

Fixes #30

This PR adds the git(::AbstractVector{<:AbstractString}) method discussed in #30 (comment).

Bonuses:

• Adds more examples to README.md.
• Adds a module docstring.
• Fixes a missing escape in the git docstring.
• Removes a duplicate test (in fact hijacks it).

[codecov]

Codecov Report

Merging #36 (4365af1) into master (b941046) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #36   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           16        19    +3     
=========================================
+ Hits            16        19    +3     

Impacted Files	Coverage Δ
src/git_function.jl	100.00% <100.00%> (ø)

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[DilumAluthge]

Fixes #30?

[GunnarFarneback]

I'd say #34 fixed #30, but yes, this adds the second item discussed there. I didn't include a git(::AbstractString) method which would be closer to the removed cmd macro, although that's a small thing to add if desired.