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
Fold opcode.{c,h} into bytecode.{c,h}
Fix leaks in jv_load_file()
Fix serious bug in handling of --argfile
Move cfunction invocation code to the interpreter loop.
Merge pull request #157 from nicowilliams/argfile-fixes

Argfile fixes
Quiet setup.sh re: tmp dir
Add libjq autoconf goo
Update .gitignore
Add mod (and setmod) operators
Document mod
Add floor operator