major front-end rewrite: re-org of module, namespace, process_definition
cleanup of a bunch of #if 0 and debug code
Merge branch 'master' into frontend-rewrite

Conflicts:
	src/ChangeLog
slowly phasing out module arguments to parser/instref functions
alias parse_local_refs to parse_global_refs, unifying them!
parser/instref API replaced module with footprint argument
Merge branch 'master' into prsim-timing-backannot

Conflicts:
	src/ChangeLog
Node now track time of last edge per value, shown in backtraces.
when initializing nodes, also reset last_edge_time[]
include last_edge_time[] in checkpoint dump
added setup/hold time spec directives to front-end, hflat output only for now
Merge branch 'master' into prsim-timing-backannot

Conflicts:
	src/ChangeLog
	src/sim/prsim/State-prsim.cc
initial implementation of setup/hold time violation checks
fix namespace comment
catch and re-throw spec exceptions in ExprAlloc
more tests
enable top-level hierarchical spec-directives like setup/hold timing
Merge branch 'master' into prsim-timing-backannot

Conflicts:
	src/sim/prsim/State-prsim.cc
partial implementation of forward-posting setup/hold timing constraints
Merge branch 'master' into prsim-timing-backannot
draft implementation of forward posting setup/hold checks, passes tests!
TODO: checkpoint preservation/restoring of active timing checks