remove the restriction that module names need to be unique per Nimble…

[Araq]

… package

[kaushalmodi]

@Araq: Can you please document in the manual and changelog as to what this change implies.

After this commit, I am seeing stuff like:

CC: stdlib_system
CC: stdlib_times
CC: stdlib_os
CC: _7_7_7_7_7_7_7_7home7kmodi7.nimble7pkgs7nimterop-#head7nimterop7plugin
CC: _7_7_7_7_7_7_7_7home7kmodi7.nimble7pkgs7nimterop-#head7nimterop7cimport

Before this commit, it looked like:

CC: stdlib_system
CC: stdlib_times
CC: stdlib_os
CC: nimterop_plugin
CC: nimterop_cimport

Ref: https://irclogs.nim-lang.org/21-04-2019.html#13:03:10

/cc @genotrance