Moved IM_MALLOC/IM_FREE/etc. to IO structure members one can set at runtime.

Added #define IMGUI_INCLUDE_IMGUI_USER_CPP to optionally include imgui_user.cpp

Minor tweaks to "Memory override" pull request

Memory override #3

Delete obsolete comments in imconfig.h

Converted all Tabs to Spaces (git diff -w shows an empty diff)

memory override attempt #2

Default "local only" clipboard handler on non-Windows platforms

Tweaks, more consistent #define names

Default Clipboard functions on Windows+ renamed ARRAYSIZE to IM_ARRAYSIZE

Fixed warnings for more stringent compilation settings. Added various small helpers.

Initial release