Bundle `Project.toml` with libraries

[sloede]

Similar to #572, this PR bundles the Project.toml file with libraries. The motivation is that otherwise it is not possible to run dynamic code in the library that is using one of the project dependencies. For example, when includeing a file from a library function, using MyPkg will currently not work even if MyPkg is listed in the [deps] section of the project dir. With this PR, using MyPkg will be possible again.

I also added a note to the docstring explaining that installing multiple apps/libraries to the same prefix is generally not possible, since they will overwrite each other's Project.toml in <prefix>/share/julia. This was already the case before for apps, I just amended the documentation for it.

[codecov[bot]]

Codecov Report

Merging #850 (9b87f8f) into master (092becd) will increase coverage by 0.04%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #850      +/-   ##
==========================================
+ Coverage   83.87%   83.92%   +0.04%     
==========================================
  Files           3        3              
  Lines         732      734       +2     
==========================================
+ Hits          614      616       +2     
  Misses        118      118              

Files Changed	Coverage Δ
src/PackageCompiler.jl	93.07% <100.00%> (+0.02%)	:arrow_up:

[sloede]

@KristofferC @IanButterworth this is ready for review from my point of view.

[sloede]

Thanks a lot for the fast response! It would be great if you could also tag a patch release.