Add missing class declaration for python bindings.
Add parse_image_filters function to avoid python bindings access the internal structs.
Export the to_wkt functions to avoid python bindings access the internal structs.
Let template parameter type same as declaration in hpp file.
Fixed the enumeration link error with msvc when build python bindings.
Add IMPLEMENT_ENUM of enum gradient_unit_e.
Only explictly defining the enumeration template class for msvc.
Merge pull request #1727 from avlee/pythonbindings

Build python bindings with msvc