feat: compiled libraries have munlib extension instead of dll/so

[legendiguess]

closes #72

[codecov]

Codecov Report

Merging #75 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #75      +/-   ##
==========================================
+ Coverage   72.13%   72.16%   +0.02%     
==========================================
  Files         109      109              
  Lines        7290     7281       -9     
==========================================
- Hits         5259     5254       -5     
+ Misses       2031     2027       -4

Impacted Files	Coverage Δ
crates/mun_target/src/spec/apple_base.rs	0% <ø> (ø)	⬆️
crates/mun_target/src/spec.rs	63.41% <ø> (+0.62%)	⬆️
crates/mun_target/src/spec/windows_msvc_base.rs	100% <ø> (ø)	⬆️
crates/mun_compiler/src/driver.rs	71.01% <100%> (+0.74%)	⬆️

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