Add ability to control path inside PEX file

[mouadino]

First off, thanks for this project it's have been helpful a lot.

Background

I am working on a project to migrate our monorepo from Make to Bazel where the repo layout is:

|-- libraries
      |-- python
.            |-- config
.                  |-- shared
                          |-- config
                                 |-- (code...)
.            |-- db 
.                  |-- shared
                          |-- db
                                 |-- (code...)
|-- services
      |-- foobar
            |--services
                 |--

However with the default behaviour of this extension, PEX files generated end up packed with a path that requires us to change all import statements in our code which is not ideal, since it's a lot of changes and we want to allow smooth migration to Bazel with as few impact on the existent code as possible, hence this changeset which allows having a slight control on the path inside the PEX files, it's meant to be used as follow:

Example

pex_binary(
    name = "service",
    srcs = glob(["**/*.py"]),
    main = "main.py",
    strip_pex_path_prefixes = [
          "libraries/python/config/",
          "libraries/python/db/",
    ],
)  

Please advise if there is a better way of doing this.

[evanj]

This is great! I actually cooked up a similar hack that I called "pythonpath" for our own Python monorepo. I'd be happy to post my change for comparison, but this looks very similar! I'd love to help get something merged upstream!