Add sample.xml status_message tests

Add some additional tests showing how message box can fill up to miss
messages.
Samples.txt, move identifier tags.

Move identifier tags to top of each item, as they were getting buried
when lots of appendices were present.  Also add missing item tag for
sample3 around line 125.
Reorder Mapping Samples section

This is a sample reordering of a long item in samples.xml.  When a
number of mappings exist in one item, this interleaves the mapping code
next to the explanation instead of leaving a puzzle at the bottom of a
long item.
Minor clean-up

Make list of mappings in Mapping Samples match style elsewhere.
Split KeyToKey MODIFIER_FLAG items.

Split into two items; add doc.
Document and reorder a few more samples
A little more cleanup and reordering.
Merge pull request #221 from merriam/master

Changes to samples.xml, adding documentation, reordering for clarity.