Release for v0.7.0

[sosey]

• fixed a text error in the display_help() so that now the correct version loads the documentation
• Windows users can now install from source. The setup will ignore the cython and xpa necessary to build the DS9 interaction, and users will only be able to use the Ginga HTML5 window, they can also use the Imexamine() functions without any graphical interface.
• Documentation updates, mostly specific information for Windows users
• Added python 3.6 to the test matrix as well as apveyor for the windows build
• Updated XPA module to v2.1.18
• Made fits checker smarter to deal with older simple fits files where EXTEND is true but there are no extensions
• fixed bug in fits loader for ds9 multi-extension FITS files, made load_fits() prefer the extension specified in the key rather than the image name

[coveralls]

Coverage remained the same at 26.464% when pulling 5614845fee8c4e077ccc2b4b248f5009909dec51 on sosey:release into 3762f1f856ec56b1f3d4c1712fd4955fbf091c8c on spacetelescope:master.