Add datadir support

[lu-zero]

Fixes #184

[codecov-commenter]

Codecov Report

Merging #229 (b603249) into master (deed1ed) will increase coverage by 0.07%.
The diff coverage is 86.48%.

@@            Coverage Diff             @@
##           master     #229      +/-   ##
==========================================
+ Coverage   84.51%   84.59%   +0.07%     
==========================================
  Files          12       12              
  Lines        1750     1785      +35     
==========================================
+ Hits         1479     1510      +31     
- Misses        271      275       +4     

Impacted Files	Coverage Δ
src/cli.rs	88.54% <ø> (ø)
src/install.rs	76.00% <72.22%> (-0.33%)	⬇️
src/build.rs	84.59% <100.00%> (+0.42%)	⬆️
src/build_targets.rs	88.88% <100.00%> (+0.13%)	⬆️
src/pkg_config_gen.rs	86.79% <100.00%> (-0.13%)	⬇️

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[lu-zero]

@naokiri would that fit your needs?

[naokiri]

@lu-zero Yes, this looks really nice. I really appreciate this feature.

[lu-zero]

If it works for your use-case I'd land it, add also doc and man support and make a new release in a week.

[lu-zero]

@naokiri did you find time to test it?

[naokiri]

Sorry I was busy and couldn't respond for a while.

For my use case I was using other configurations name for directory names and I needed a similar configuration like this PR
#237

[lu-zero]

Let me land this and then add upon it.