Tests from Scintilla and Francois added.
New Feature for BoostRegexSearch: force allow match at start

This ignores the "continuation-search" check, and always allows a match at the start of the search range.  This is needed for replace functionality.
Replace function now working

Issue was with replace needing to "double-check" that the
selection still matches, and therefore needs to force to
allow an empty match at start point. It happened to work
previously when clickable links was enabled, as between
each replace was a search to check if any clickable links
had been introduced, and therefore the "replace" search
was never flagged as a continuation search by the
boostregexsearch class.
Mark All functionality fixed.

Scintilla 2.27 doesn't like INDICATORFILLRANGE call with
a zero length. Further indicators on the same line don't get
drawn.