Fix Fl_Help_View buffer overflow (STR #3275).

This version works much better than the previous one:

 - fixed buffer overflow ("stack corruption")
 - fixed potential long text truncation
 - fixed tab formatting at line start or any offset divisible by 8
 - better handling of HTML entities (aka quoted characters)
 - code simplifications, e.g. HV_Edit_Buffer::cmp() + width()

Todo:

 - improve and standardize handling of HTML entities
 - more tests

Missing features and known bugs:

 - strike out text (not implemented)
 - table and horizontal line formatting issues (STR #3227)



git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@11745 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

CHANGES

@@ -100,6 +100,7 @@ CHANGES IN FLTK 1.3.4					RELEASED: ??? ?? 2016
 
 	Bug fixes
 
+	- Fixed Fl_Help_View buffer overflow (STR #3275).
 	- Fl_Browser now correctly adjusts its scrollbars when the default
 	  text size is changed with textsize(int) (STR #3057).
 	- Fixed Fl_Text_Display/Fl_Text_Editor slow scrolling, line number

FL/Fl_Help_View.H

@@ -187,7 +187,7 @@ struct Fl_Help_Target {
      - macr micro middot
      - nbsp not Ntilde ntilde
      - Oacute oacute Ocirc ocirc Ograve ograve ordf ordm Oslash oslash Otilde otilde Ouml ouml
-     - para premil plusmn pound
+     - para permil plusmn pound
      - quot
      - raquo reg
      - sect shy sup1 sup2 sup3 szlig