Added an example hexagonal map

Based on public domain tiles by pixel32, found at:

http://opengameart.org/content/pixel-hex-tilesets-enhanced
Removed some unused defines
Added a CSV export plugin

This plugin only exports the first tile layer. Tiles are written out by
their index in the tileset, or by their "name" if this custom property
is set on them. Empty cells are written out as -1.

Closes #277
Eliminate some building issues on Windows

- Use --large-address-aware instead of /LARGEADDRESSAWARE with MinGW
- Adjust an #include in libtiled/objectgroup.cpp