install: Expose test + docs requirements, encourage use of virtualenv

[EricCousineau-TRI]

• Use setuputils.setup(..., extras_require)
• Organize imports according to PEP8 (builtin, 3rd party, then 1st party)

For extras_require: https://setuptools.readthedocs.io/en/latest/setuptools.html#declaring-extras-optional-features-with-their-own-dependencies Saw this when looking at trimesh: https://github.com/mikedh/trimesh/blob/4cacbffcd9bd1a637bf05b638bc3376464e3577b/setup.py

For PEP8 imports: https://www.python.org/dev/peps/pep-0008/#imports

[EricCousineau-TRI]

Install:

• before:

  

• after:

  

Docs:

• before:

  

• after:

  

[EricCousineau-TRI]

Thanks! I rebased - I think it'll work?

[iMichka]

Thanks @EricCousineau-TRI !