Prototype implementation of Sage wrappers for FLINT generic rings TODO: (see also comments in code) - more coercions and constructions - more flexible handling of T_UNKNOWN - inline element structs in Element object for at least some contexts (Element subclasses?) - systematically wrap gr API - more conversions from/to usual Sage objects (including fexpr <-> SR?) - FlintPolynomial class (as subclass of FlintElement or Polynomial?) - FlintMatrix - FlintMPolynomial - element subclasses with type-specific methods where relevant - adapters for viewing Sage objects as Flint generic ring elements - documentation, tests - ...