Ditz issue update
Makefile size output, dump-public symbols
Dump leaked duk__ symbols in dump-public
Add DUK_SINGLE_FILE to single file duktape.h

This is needed by symbol visibility macros.
Missing static declarations
First draft of symbol visibility macros

For GCC 4+ these now produce a nice clean build when compiling the split
compiler source files.  Without these, the result is quite messy.
Some internal documentation on symbol visibility
Code issues section heading trivia
MSVC symbol visibility macros, not tested
DUK_EXTERNAL test
MSVC symbol visibility note