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
Fix isodata-thresholding according to Zachary Pincus
Return to old function name threshold_isodata
Account for case when image only contains one unique value
Fix test cases which are now wrong due to previous binning error
Improve test coverage
Fix return value description
Test missed line for coverage
Merge pull request #1090 from ahojnnes/isodata-fixes

Fix isodata-thresholding according to Zachary Pincus
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