DOC: Fixed spacing in the XML to JSON script

GenerateDocumentation.groovy has been updated to add a leading
space for 'ulink' nodes and a trailing space for 'ulink' and
'ref' nodes.  In the former case, it checks if a space precedes
it.  The latter case can lead to an extraneous space, if the
node is immediately followed by a period or other punctuation.

Change-Id: I279d3a6d73a8754abe8baf855c4f00f0a543b0e8
Convert <sp\> tag to a space

This caused significant problems with the parsing of comments around
code blocks.

Change-Id: I7bf498bed3fed65a71ec8f8bc81de3275f15b69b
Updating JSON doc string from ITK 4.6 with spacing corrections.

This includes spacing in code blocks and spaces round links and refs.

Change-Id: I945d03d8be98aebdd187ae41864c072b5dd13032
Merge branch 'SIMPLEITK-568_FixSpacingInDoxygenFromITK' into release

* SIMPLEITK-568_FixSpacingInDoxygenFromITK:
  Updating JSON doc string from ITK 4.6 with spacing corrections.
  Convert <sp\> tag to a space
  DOC: Fixed spacing in the XML to JSON script

Change-Id: I06225796445ea6c195f5025205336590fecfa82b