Refactor the API to make it more reusable

[DilumAluthge]

This pull request is a major refactoring of both the public API and the private (internal) API.

Closes #87

[codecov]

Codecov Report

Merging #88 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            master       #88    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           14        17     +3     
  Lines          177       311   +134     
==========================================
+ Hits           177       311   +134     

Impacted Files	Coverage Δ
src/SimpleContainerGenerator.jl	100.00% <ø> (ø)
src/assert.jl	100.00% <ø> (ø)
src/backups_of_simplecontainergenerator.jl	100.00% <ø> (ø)
src/generate_helper_files.jl	100.00% <ø> (ø)
src/generate_install_packages.jl	100.00% <ø> (ø)
src/generate_packagecompiler_install.jl	100.00% <ø> (ø)
src/generate_packagecompiler_run.jl	100.00% <ø> (ø)
src/generate_precompile_execution.jl	100.00% <ø> (ø)
src/julia.jl	100.00% <ø> (ø)
src/utils.jl	100.00% <ø> (ø)
... and 10 more

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