copy particle position data to persistently mapped vertex buffer
update terrain height buffer in changed ranges only
enable back face culling for the terrain
update terrain type buffer only as needed
less dramatical abort if wrong working directory is set
replace glBufferStorage (requires OpenGL 4.4/ ARB_multi_bind)
fix particle vbo update, don't try to map the buffer persistently (pre opengl 4.4)
use smaller texture formats (needs testing on different platforms)

- could improve rendering performance
Merge pull request #118 from lanice/buffer_update_performance

Buffer update performance