Reviewing GetTime() functionality

OpenAL Soft backend is still available in audio module, I'm thinking if
exposing it for building in some way or just left it there for advance
users to switch to it manually in case of necessity...

Updated raylib version to 1.9-dev for development pourposes.

Next raylib version is planned to implement a big amount of changes, so
the version bump.

Feature macros need to be defined before #including any headers,
preferably through the build system, but this is good enough.

Fixes a compile error on my fork's Travis CI.

Now header is truly multiplatform...

Actually still a small pending check on XBOX gamepad controls that
hopefully will be removed with next GLFW 3.3

Corrected issue with RPI_CROSS_COMPILE

SetWindowTitle()
GetExtension()

Now it works great with reviewed maths

Some other tweaks...

Now it should be coherent with OpenGL math standards

Exposed some raymath useful functions to raylib API

Consistent with similar functions in raymath

...to avoid possible conflicting symbols

If we compile with c99 without gnu extensions (gnu99) we need this
define, to have CLOCK_MONOTONIC and similar macros available

Comments to create transparent framebuffer on RPI,
when activate you see though full screen window the console below!

useful when using FLAG_WINDOW_RESIZABLE.

enum LogType could require some revision...

Replaced old GetExtension() function
Make IsFileExtension() public to the API