issue_6517: Emoji support

Added issue support for the different output types.

- Sources of the emoji
  - based on the Unicode definition v11.0:
    - https://unicode.org/emoji/charts/full-emoji-list.html
    - http://www.unicode.org/emoji/charts/full-emoji-modifiers.html
  - github definition list:
    - https://api.github.com/emojis

- Input of emoji: :<test>: with the restriction that direct after the opening colon and direct before the closing colon no space is allowed
  - doctokinizer.l, adding detection of emoji and new command `\:`
  - doktokinizer.h, adding "word" type  TK_EMOJI
  - docparser.* handling of new "word" type TK_EMOJI (analogous to HTML Entities), handling of new command `\:`
  - cmdmapper,cpp, cmdmapper.h, adding new command `\:`
  - htmlentity.cpp, adding new definition required for new command `\:`

- Emoji
  - emoji.cpp, emoji.h, class for handling emoji analogous to HTML Entities, including small directions on how to update the code when a new emoji is defined. Not everything is converted to lowercase for comparison and accents are removed.
  - doxygen.cpp possibility to create list of supported emoji

- handling emoji for output types (analogous to HTML Entities), see documentation for different output types
  - docparser.h, *docvisitor.*
  - rtfdocvisitor.* converting output to UTF-16 (based on http://scruss.com/blog/2017/03/12/in-the-unlikely-event-you-need-to-represent-emoji-in-rtf-using-perl/)
  - latexdocvisitor.*, handling arguments for emoji in output (see also latexgen.cpp for meaning of the arguments of doxygenemoji).
  - latexgen.cpp, adding new latex command for doxygen (doxygenemoji) and prevent too many open file (code before documentclass)
  - config.xml, definition of `LATEX_EMOJI_DIRECTORY` with path to images required for LaTeX output

- Documentation:
   - emojisup.doc, user description
   - commands.doc, description of new command `\:`
   - index.doc, reference to emoji chapter
   - xmlcmds.doc, adjust reference to next chapter as a new chapter is added
   - Doxyfile*, adding emoji chapter

Build system
  - CMakeLists.txt adding new files

1 files changed, 18 insertions, 2 deletions

diff --git a/src/docparser.h b/src/docparser.h
index 68f9fc1..8aca82d 100644
--- a/src/docparser.h
+++ b/src/docparser.h
@@ -140,7 +140,8 @@ class DocNode
                 Kind_HtmlBlockQuote = 49,
                 Kind_VhdlFlow       = 50,
                 Kind_ParBlock       = 51,
-                Kind_DiaFile        = 52
+                Kind_DiaFile        = 52,
+                Kind_Emoji          = 53
               };
     /*! Creates a new node */
     DocNode() : m_parent(0), m_insidePre(FALSE) {}
@@ -454,7 +455,7 @@ class DocSymbol : public DocNode
                    /* doxygen commands mapped */
                    Sym_BSlash, Sym_At, Sym_Less, Sym_Greater, Sym_Amp,
                    Sym_Dollar, Sym_Hash, Sym_DoubleColon, Sym_Percent, Sym_Pipe,
-                   Sym_Quot, Sym_Minus, Sym_Plus, Sym_Dot
+                   Sym_Quot, Sym_Minus, Sym_Plus, Sym_Dot, Sym_Colon
                  };
     enum PerlType { Perl_unknown = 0, Perl_string, Perl_char, Perl_symbol, Perl_umlaut,
                     Perl_acute, Perl_grave, Perl_circ, Perl_slash, Perl_tilde,
@@ -475,6 +476,21 @@ class DocSymbol : public DocNode
     SymType  m_symbol;
 };
 
+/** Node representing a n emoji */
+class DocEmoji : public DocNode
+{
+  public:
+    DocEmoji(DocNode *parent,int  s) : 
+      m_symbol(s) { m_parent = parent; }
+    int  emoji() const     { return m_symbol; }
+    Kind kind() const          { return Kind_Emoji; }
+    void accept(DocVisitor *v) { v->visit(this); }
+    static int  decodeEmoji(const QCString &symName);
+
+  private:
+    int   m_symbol;
+};
+
 /** Node representing some amount of white space */
 class DocWhiteSpace : public DocNode
 {