allow str in subroutine signature

[irmen]

Currently you can use str only in asmsub signature, for regular subroutines the compiler gives an error about that reference types should be an uword.

examples/test.p8:10:0: ERROR Pass-by-reference types (str, array) cannot occur as a parameter type directly. Instead, use an uword to receive their address, or access the variable from the outer scope directly.

This should be fixed so that str can be used in signature .
(The issue is related to the way subroutine params are treated as local variables.)

Ideally we do the same for array types but that's a different issue, one that is difficult to solve because the compiler now treats array vars as a direct (name) reference to the array in memory. Passing different arrays in the place of an array var can't be done right now.

[irmen]

(Fixed in 7.2)