Added tools for running/stopping apk on android

Added tools for running/stopping apk on android
    devtools.sh
Added tangent and bitangent calculation for Mesh

Added tangent and bitangent calculation for Mesh
    src/graphics/Mesh.cpp
    src/graphics/Mesh.h
Minor change to renderer interface

Minor change to renderer interface
    src/core/MainManager.cpp
    src/graphics/GraphicsManager.cpp
    src/graphics/Renderer2dImage.cpp
    src/graphics/Renderer2dImage.h
    src/graphics/RendererInterface.h
Added simple FpsCounter class

Added simple FpsCounter class
    src/util/FpsCounter.cpp (+)
    src/util/FpsCounter.h   (+)
Added pixel perfect charmap based text render

Added pixel perfect charmap based text render
    assets/images/gnsh-bitmapfont.png (+)
    assets/shaders/render2dtext.frag  (+)
    assets/shaders/render2dtext.vert  (+)
    src/core/MainManager.cpp
    src/core/MainManager.h
    src/graphics/Renderer2dText.cpp   (+)
    src/graphics/Renderer2dText.h     (+)
Updated devtools target for android assets-only

Updated devtools target for android assets-only.

If only assets change, using this this target will repack and resigned the
modified assets. This shaves off a few seconds.

    devtools.sh
Added extensive OpenGL debugging functions

Added extensive OpenGL debugging functions
    src/graphics/GlCheck.cpp
    src/graphics/GlCheck.h
Added flite library for text to speech synthesis

Added flite library for text to speech synthesis

Added a heavily stripped down version of flite-1.4 from
http://www.festvox.org/flite/

To see changes from original source repository see:
    external/flite/sdl2-cross-changes.md   (+)

Other changes:
    README.md
    external/flite/ACKNOWLEDGEMENTS (+)
    external/flite/COPYING          (+)
    external/flite/README           (+)
    external/flite/include/*        (+)
    external/flite/lang/*           (+)
    external/flite/main/*           (+)
    external/flite/src/*            (+)