Added FunctionManifoldChart
Added two test files for FunctionManifoldChart
Added changelog
Added relative tolerance, and better comment for owns_pointers.
Refactored FunctionManifold.
Refactored ManifoldChart to ChartManifold.
Made FlatManifold tolerance relative.
Merge pull request #67 from luca-heltai/function_manifold_chart

Function manifold chart