Parse more package items

Rework lexical support for PACKAGE_IDENTIFIER so that the lexor
can help with package scoped identifiers.

Pform package types and package functions up to elaboration.
parameter table in ivl_scope_s uses vector instead of C arrays.
Elaborate parameters, tasks and functions in packages.

Get the elaboration to happen all the way to the ivl_target
interface.
packages can contain variables.
Fix handling of struct members for variables imported from packages.
Handle tasks in packages.
Update some copyright notices.
Merge branch 'work13b'
Merge branch 'master' of github.com:steveicarus/iverilog