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, 15 insertions, 0 deletions

diff --git a/src/htmldocvisitor.cpp b/src/htmldocvisitor.cpp
index 6e0c62d..0af5b16 100644
--- a/src/htmldocvisitor.cpp
+++ b/src/htmldocvisitor.cpp
@@ -34,6 +34,7 @@
 #include "filedef.h"
 #include "memberdef.h"
 #include "htmlentity.h"
+#include "emoji.h"
 #include "plantuml.h"
 
 static const int NUM_HTML_LIST_TYPES = 4;
@@ -234,6 +235,20 @@ void HtmlDocVisitor::visit(DocSymbol *s)
   }
 }
 
+void HtmlDocVisitor::visit(DocEmoji *s)
+{
+  if (m_hide) return;
+  const char *res = EmojiEntityMapper::instance()->html(s->emoji());
+  if (res)
+  {
+    m_t << res;
+  }
+  else
+  {
+    err("HTML: non supported Emoji-entity found: %s\n",EmojiEntityMapper::instance()->html(s->emoji()));
+  }
+}
+
 void HtmlDocVisitor::writeObfuscatedMailAddress(const QCString &url)
 {
   m_t << "<a href=\"#\" onclick=\"location.href='mai'+'lto:'";