Custom build.rs path support, local time offset support, updated gix dep

[CraZySacX]

• Updated gix to 0.48.0
• Added support for specifying a custom build.rs location.
• Added support for using a local offset for date/timestamp display.
  NOTE - Using a local offset will likely cause failures on Unix systems due to the Soundness check that the time crate performs. I don't want to introduce unsoundness support to vergen.

Fixes #214
Fixes #222

[codecov]

Codecov Report

Merging #223 (92615a5) into master (c51c8d3) will decrease coverage by 0.27%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #223      +/-   ##
==========================================
- Coverage   98.44%   98.17%   -0.27%     
==========================================
  Files          23       23              
  Lines        1609     1645      +36     
==========================================
+ Hits         1584     1615      +31     
- Misses         25       30       +5     

Impacted Files	Coverage Δ
vergen/src/feature/git/cmd.rs	97.22% <75.00%> (-0.87%)	⬇️
vergen/src/feature/git/git2.rs	97.47% <75.00%> (+0.59%)	⬆️
vergen/src/feature/git/gix.rs	96.51% <75.00%> (-1.08%)	⬇️
vergen/src/emitter.rs	93.83% <85.71%> (-1.06%)	⬇️
vergen/src/feature/build.rs	100.00% <100.00%> (ø)
vergen/tests/build_output.rs	100.00% <100.00%> (ø)
vergen/tests/git_output.rs	100.00% <100.00%> (ø)

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