Unify frame and data stacks
Unify all stacks. Passes tests, but needs cleanup.
Simplify frame logic.
Clean up lots of stack and frame logic.

Move frame defs to execute.c
Merge branch 'stack-refactor'

Conflicts:
	execute.c
Merge branch 'stack-refactor-merge'
Remove some initialise-to-zero code.

This lets valgrind find more bugs - if a field isn't given a
well-defined value valgrind will now find it instead of seeing it
set to zero with memset.
Saner build instructions in README.md

Closes #144
Simplify block functions for variables
Quiet setup.sh re: tmp dir
Add libjq autoconf goo
Set libjq.so version to 1.4.0
Don't export jq_parse() and jq_parse_library()
Install jv.h and jq.h and rm now empty headers
Add jv_mem_uninitialised to libjq.map
Fix serious bug in handling of --argfile
Fix leaks in jv_load_file()