update:
- update version info for 3.1
- aiGetVersionRevision will now return the git tag.

Signed-off-by: Kim Kulling <kim.kulling@googlemail.com>
OgreImporter: Started cleanup and refactoring. Aim is to get this into a shape that its easy to read and understand before I start making any new features.
OgreImporter: Continue cleanup.
OgreImporter: Remove unnecessary m_currentX state. Improve and clean OgreMaterial: split tech/pass/texture_unit to their own functions. Document missing features and potential bugs. Improve the original authors 'detection from texture filename' logic (enabled with AI_CONFIG_IMPORT_OGRE_TEXTURETYPE_FROM_FILENAME). Add generic detection from texture unit name, which is commonly used in Ogre materials.
OgreImporter: Rewrote documentation for AI_CONFIG_IMPORT_OGRE_MATERIAL_FILE and AI_CONFIG_IMPORT_OGRE_TEXTURETYPE_FROM_FILENAME to reflect the current logic. And to be honest the earlier one was very confusing english and was not very clear what is happening with these config options.
OgreImporter: Rename .hpp to .h. Shuffled parsing utils to a single file.
OgreImporter: Forgot to rebuild after filename changes so broke the build. Fix includes, add include guards and ASSIMP_BUILD_NO_OGRE_IMPORTER to missing places.
OgreImporter: Cleanup and bugfixes to OgreSkeleton.cpp. This was actually so badly broken that it did nothing if the mesh referenced a binary skeleton. Now logs a warning for this case and tries to read from .skeleton.xml like the original author intended it to work. The assimp skeleton is still broken, I will fix that later on when I (eventually) get to that part of the code.
OgreImporter: Cleanup skeleton related code and code that populates the assimp scene. Tested skeleton/animation imports and it seems to work correctly now.