pil_plugin can import and export from memory

- added capability to import and export to PIL Image
  objects, not just files - allows for converting
  to and from PIL image objects without writing
  to disk
- no unit test yet
added tests for roundtrip export and import

- and corrected error in imexport - wasn't using imsave code
  correctly
- split imsave into imsave and imexport functions to reuse
  imsave code
added a space character to trigger travis build
fixed bad indent
improved name of pil import/export functions

- to make it clear what the functions actually do:
  ndarray_to_pil() and pil_to_ndarray()
- as per code review feedback
- updated tests to use the new function names

- incoming change to pil_plugin assumed PIL Image
  objects will always be from files; this is
  not always true anymore. Now pil_plugin
  checks to see if the Image came from a file
  before trying to close its associated file.
reformat comments to be standard format

- clarified function names
- comments in standard format
- removed extra blank line
- as per code review feedback
added Adam Feuer (myself) to contributors file

- as per code review feedback from @stefanv
updated imread parameters comment to standard format

- with 'str' file type (instead of 'string')
removing trailing space (PEP8 formatting)
explicitly checking for None as per code review feedback

- instead of implicit (non-truthy) test
removed trailing blank line in comment
Merge pull request #1083 from adamfeuer/import_export_pil_image_objects

pil_plugin can import and export PIL image objects from memory