Normalize ctor initialization list style.
Don't convert const pointers to mutable ones.
Add ctor_of() to push class constructors.

Not quite sure if the std::forward<Args> has any effect in ctor_of.
APOLLO_TO_RAW_FUNCTION: Don't automatically apply &.
Simplify ctor wrapper & add get_raw_ctor_wrapper.

The latter is necessary for MSVC, which chockes on decltype applied to
(variadic?) template functions.
Add export_class(), finding error in table_setter.
Rewrite create_table.
Move ctor wrapper to function.hpp.

Fixes build on compilers with proper two-phase lookup (i.e. non-MSVC). Also,
this makes somewhat more sense: You can push (though not call) an constructor
w/o object support, but not w/o function support.
Fix clang build + warnings.
Add experimental Travic CI support.