Added sectionlist type for [[name]] table list syntax highlighting.
sections and sectionlists are now defined as block statements.
Added highlighting of invalid section names.
Added an additional invalid section name case.
Got carried away...  multiple things.

Added the three additional string types ('...', '''...''' and
"""...""").  Escape characters are highlighted in double quoted strings
and back slashes at the end of a line in a multi line double quoted
strings.  Strictly following the wording of the TOML description nothing
is allowed to trail table or table array declarations as implied by
"They appear in square brackets on a line by themselves."  Finally (I
think) pattern names containg "section" were modified to "table" as the
spec officially refers to them.

This is pretty much feature complete for my needs.  I'm probably done at
least for now.
Merge pull request #2 from rnd42/master

Much better highlighting.