Makefile size output, dump-public symbols
Add DUK_SINGLE_FILE to single file duktape.h

This is needed by symbol visibility macros.
Add some 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.

MSVC symbol visibility macros are based on feedback from David Demelier.
They seem to now allow a Windows DLL build (__declspec(dllimport) and
__declspec(dllexport)).
Refactor symbol visibility macros a bit
Some internal documentation on symbol visibility
Add DUK_EXTERNAL_DECL to public API calls
API macro note: limitation with no variadic macros
API header DUK_OPT_NO_FILE_IO fix, other trivia

- Make duk_dump_context_{stdout,stderr}() a comma expression macro instead
  of a do-while-macro to allow use in expressions, e.g.
  "(void) duk_dump_context_stdout()"

- Fix trivial bug for DUK_OPT_NO_FILE_IO
Add symbol visibility checks to code policy util

This required some awkward changes because the symbol visibility check needs
access to the previous line in some cases.
Symbol visibility changes for initdata
Symbol visibility changes for code and headers
API testcase for dll link test
Release note: DUK_OPT_NO_FILE_IO fix
Use __declspec(dllexport) for DLL build on Windows

This seems to be common practice in other libraries (e.g. Curl).
Document DUK_OPT_DLL_BUILD
Release note: DUK_OPT_DLL_BUILD
Merge branch 'symbol-visibility-macros'

Add symbol visibility macros for header definitions and actual declarations.
These are concretely needed for Windows DLL build support (__declspec(dllexport)
and __declspec(dllimport)).  These macros will also be useful for controlling
symbol visibility when e.g. duk_js_compiler.c is split into multiple files.

Add DUK_OPT_DLL_BUILD feature option for a DLL build.  It is critical for
Windows build to enable __declspec(dllexport)/__declspec(dllimport).