This postpones the semantic pass over the generic's body until
the generic is instantiated. There are several pros and cons for
this method and the capabilities that it enables may still be possible
in the old framework if we teach it a few new trick. Such an attempt
will follow in the next commits.
pros:
1) It allows macros to be expanded during generic instantiation that
will provide the body of the generic. See ``tmacrogenerics``.
2) The instantiation code is dramatically simplified. Dealing with unknown
types in the generic's body pre-pass requires a lot of hacky code and error
silencing in semTypeNode. See ``tgenericshardcases``.
cons:
1) There is a performance penalty of roughly 5% when bootstrapping.
2) Certain errors that used to be detected in the previous pre-pass won't
be detected with the new scheme until instantiation.
For example, this allows you to pick up a proc with a specific signature from
an overload set.
bugfix: nimrod generated invalid code when a RVO function had a single
compile-time param
bugfix: nkHiddenDerefs were not neutralised properly for indirect proc calls
See the section `do notation` in the manual for more info.
* nkMacroStmt has been removed
Macro statements are now mapped to regular nkCall nodes.
The support for additional clauses (such as else, except, of, etc)
have been restored - they will now appear as additional arguments
for the nkCall node (as nkElse, nkExcept, etc nodes)
* fixed some regressions in the `is` operator and semCompiles
Other fixes:
* bind once is now the default for type classes as documented in the manual
* fixes an issue in template overloading (erroneous ambiguity when different typedesc params were used)
