MeshTools: renamed clean() to removeDuplicates().
MeshTools: this can be moved instead of copying.
MeshTools: added duplicate() utility for creating non-indexed array.
No need to add `#line` directive also before `#version` line.
Properly number shader sources.

Previously the sources were numbered 1, 3, 5 etc., which is wrong.
Shaders: ported MeshVisualizer to not require geometry shader.

Wireframe width and smoothness isn't ported yet, because I don't fully
understand the behavior of standard derivatives in fragment shader.
Fixed comma at the end of enumeration list.
GCC 4.6 compatibility: weird name conflicts. WTF.
Moved BufferTextureFormat enum before the class.

Just to make merging into the compatibility branch easier.
SceneGraph: use `virtual` where it hurts less.

Having `virtual` destructor in less templated base is better than having
it repeated in five times more subclass specializations.
Shapes: simplified collision dispatch implementation with macro.
Shaders: use Context::isVersionSupported() instead of ad-hoc solution.

Also removed redundant branching for ES.
Shapes: overlooked `typename`.

Spotted by good ol' GCC 4.4. Newer compilers don't bother with that
verbosity at all.
Oh yeah, coding while drunk.

F'ed up in c2a5919b5a7f78dbcf280a3dff2ec15dac7b12dc.
NaCl's newlib doesn't have std::to_string().
Fixed resource import headers.
Shaders: really ported MeshVisualizer to ES.
Shaders: allow default construction of MeshVisualizer.

While it doesn't make any sense, it is more convenient than writing {}
when testing it.
Added section for ES2-compatibility-only features into documentation.
Added ES2-only support for GL_LUMINANCE{,_ALPHA}.

It is deprecated, but many ES2 implementations don't support
EXT_texture_rg, thus this is the only way to have single- and
two-component textures without wasting precious memory. The enum value
isn't exposed on desktop OpenGL and ES3. GL_ALPHA is not supported, as
it doesn't bring any new functionality (it is also single-component
and thus can be interchanged with GL_LUMINANCE).