Add headers and precompiled libraries for libcurl support on all platforms
 - libcurl has platform-specific header files because it performs architecture-related checks at compile time
 - cross-compilation of libcurl is prohibitively difficult, keeping precompiled static libraries is much easier
Add VertexLayout class, needs comments
start work: geoUtil
a utility projection class and mercprojection class
revision to projection utility class
typo correction from #pragma one to #pragma once
Merge pull request #7 from tangram-map/geoUtil

An abstract projection class and child mercprojection class
Add VboMesh: a drawable collection of geometry using a vertex buffer and (optionally) index buffer
Fix some types in VertexLayout
Fix some types and make functions const where applicable in ShaderProgram
Add example usage of VboMesh to tangram test program
VboMesh now holds a shared_ptr to a VertexLayout object, which will be shared across many meshes
updated initialization of viewModule
updated MercProjection constructor
updated viewModule to include a member for projection, default sets it to mercator projection, unless some other projection is specified.
added a method to get the reference of the current mapProjection
Use reference for iterating over a list
Use a shared_ptr to pass ShaderProgram as a function argument
Clarify the use of 'offset' in VertexLayout
Add destructor for VertexLayout