Fixing struct tags and removing the Rest field for left over tiff.Tag
Prefixing baseline image files with baseline_
s/process/decode
Removed obsolete TODO
s/Interoperability IFD/InteroperabilityIFD
Removing "Interoperability IFD" since it belongs in exif.  Adding EpsonPrintImageMatching for now.
Unify the interfaces in tiff & bigtiff to one compatible set.

- Make tiff.TIFF an interface.
- BigTIFF can now use the same interfaces as regular TIFF.
- Add version registration and allow custom parsers per version.
- Remove custom interfaces from BigTIFF and replace them with the same
  ones from tiff.
- This allows for great simplification in tiff85 by removing the parse
  function in favoring of registering a version and using the core tiff
  package's ParseTIFF.  Other packages that custom version, but behave
  just like a regular tiff will benefit from this.
Changing magic strings to have "Magic" in the name for clarity.
Moving const references from const.go to tiff and bigtiff (they were small anyways).
Delete const.go and bigtiff/const.go now that they are empty.
Change Parse to use a ReadAtReadSeeker.

Otherwise, Parse was wrapping the io.Reader to make a ReadAtReadSeeker,
but this was after the first 4 bytes had already been read.  So, offset
values were wrong since the new start was 4 off from the actual
starting point.
Fixing struct tags for exif gps