First commit of basic indent commands

Commands:
* Indent Tags: reformats the selection/document so that tags are all on
their own line. It will try to put the close tag on the same line as the
open tag if they were in the original, but only ever 1 tag per line.
Comments are treated as plain text and won't be moved around.
* FjLib-XML: Indent Tags and Comments: As Indent Tags but comments are
treated as self closing tags and formatted onto their own lines.
* Strip Blank Lines: Not strictly to do with XML so I should pull it out
into another project, but this just removes all lines which are
whitespace only from the selection/document.