Change naming for method implementations.

Change the naming conventions for the functions which implement
clownfish methods, adding a suffix "_IMP" rather than relying on
case changes.

Before: prefix_Foo_do_stuff
After:  Prefix_Foo_Do_Stuff_IMP

This change should make it harder to confuse the method invocation
(static inline) function with the (concrete) function which implements
the method for a specific class.

The old naming style is temporarily preserved as an pound-define alias
until all existing classes can be transitioned.
Change capitalization of host OVERRIDE wrappers.

Use the capitalization conventions of Clownfish methods rather than
Clownfish inert functions.

Before: prefix_Foo_do_stuff_OVERRIDE
After:  Prefix_Foo_Do_Stuff_OVERRIDE
Transition Clownfish runtime to `_IMP`.

Change the names of C functions which implement Clownfish methods within
the Clownfish runtime parcel to use the new-style names with an `_IMP`
suffix.
Update Clownfish docs for _IMP.

Change the documentation for naming conventions of method
implementations.
Transition Clownfish TestHarness to _IMP.
Migrate Clownfish runtime unit tests to _IMP.
Fix misspelling of method imp Prefix.

Will be rolled into earlier commit before merging to master.
Address direct invocation of method imp funcs.

Where the implementing functions for methods are invoked directly
within the Clownfish runtime, either change the spelling to the
new-style with _IMP suffix, or change the call to use dynamic
method invocation.
Migrate C bindings for Clownfish runtime to _IMP.
Address a few unused var warnings.
Migrate Clownfish runtime Perl bindings to _IMP.