Patches to revive p6-pb

This pull request is the first major chunk in the process of reviving p6-pb so we can continue active development.  These patches mostly get the project to a decent state to build on, without any major functional improvements yet.

I've ordered the patches into subsets, as follows:

Remove bitrot and fix minor bugs:
45fac6e Convert bless(*, ...) to bless(...) to follow a Perl 6 spec change
0472cc9 Fix type declarations for Positional attributes in all PB::Model::* classes
1c7a65d Bug fix in PB::Actions: An int-lit should return an Int, not a Num

Style, consistency, readability:
5818831 Simplify some complex expressions that can be replaced with builtin operators
3fa1023 Consistently use abbreviated colonpair syntax for named arguments in lib/
f4b4854 Be consistent about explicit ! and ? for params in new() declarations
66b7128 Fix an incorrect EXPORT usage comment
81eba3d Add newline at end of module files that are missing it

Improve testability:
dac23c5 Test against official .proto tests separately from local grammar tests
2a5d70f Add done() calls to end of test files so prove can detect end-of-tests

Fix equality / equivalence confusion (and a test suite bug thus uncovered):
7302e7e Provide infix:<eqv> comparison multis instead of infix:<eq>
2d8e7a6 Convert test helper functions to use eqv comparisons instead of eq
cd8fec8 Fix ok...eq and nok...eq tests to use is_eqv and isnt_eqv, respectively.
d0f39b7 Fix float tests to compare against Num (not Rat) constants