clarify getCurrentViewport

currentViewport was used as a shadowing local variable - this change is purely for code clarification.
GPU optim # 1

store uniform locations even if location returns -1. If uniform location would not be stored, many unnecessary glGetUniformLocation requests would be issued on every draw call.

This is especially pronounced if custom shaders were used which do not define the built-in shader uniforms.

Since the uniform locations cannot change once a shader is linked, a failure to look up the uniform on the first frame will also mean a failure to look it up on every following frame. By catching this early, we don't incur a driver overhead penalty per uniform per frame.
GPU optim #2

native viewport caching.

Since most apps just use one render viewport, it pays off to cache the render viewport and only issue a glGetInteger Query should the viewport have changed.

Before this, the viewport would have been queried twice a frame at least.

glGetInteger() has the potential for high driver overhead, since worst case the pipeline needs to be flushed before the query can return, and the CPU can continue issueing commands.
ofMath documentation grouping, and small fixes
Merge ofSite documentation with ofVec2f
Added OF_DEPRECATED on some old ofVec2f functions that have been marked since 006
Small fix in ofVec2f doc
Added some see also to ofVec2f
ofVec2f doc fixes
Reorganized ofVec2f operators for better overview in documentation
Added images to ofVec2f
Documented ofVec3f from ofSite docs

Some old methods have also been marked deprecated, since they have been that for a very long time
Document ofVec4f. Adding named groups, and deprecate some old functions
ofMatrix4x4 documentation and named grouping
ofMatrix3x3 documentation
ofQuaternion documentation
quaternion doc cleanup
Merge branch 'documentation-math' of https://github.com/HalfdanJ/openFrameworks into documentation-math
Documentation updates to ofMath.
Merge pull request #3 from bakercp/documentation-math

Documentation math