Rather than the very C-like API we currently have, accepting a void* and
a length, let's take a Bytes object instead. In almost all existing
cases, the compiler figures out the length.
All the elliptic curve implementations had a long list of private
methods which were all stored in a single .cpp file. Now we simply use
static methods instead.
These changes generalize the interface with an elliptic curve
implementation. This allows LibTLS to support elliptic curves generally
without needing the specifics of elliptic curve implementations.
This should allow for easier addition of other elliptic curves.
