Refactor parser. Rename 'test-builder' to 'test-scan'.
Preparation for further parser redesign: Change parser node list type, begin moving fields to new op ref type, simplify memory management. No functional change. * Simplify memory handling by using the mempool for all parse data node allocation. Freeing becomes trivial. Also include the symtab in the produced parse (since it depends on the mempool), which may suit future needs. * Add new op ref type, op list wrapper type. Use instead of ptrlist in parser; the parseconv output is the same. * Move label from op data node to op ref node. Also fix bug in handling of deferred step, which caused crash now but didn't before. * Move link_type from op data node to op ref node. Also rearrange code to silence old warning about possible variable use before assignment. Rename 'test-builder' to 'test-scan', now built with `make tests`. Minor correctness improvement in parseconv. Return failure instead of success count in SAU_build(). Increase version to v0.3.4b. Clean up .gitignore. Change log: * 2019-11-11: Set version to v0.3.4-beta. * 2019-11-12: Change SAU_build() return value. * 2019-11-28: Rename 'test-builder' to 'test-scan', and remove old program names from .gitignore. * 2019-12-01: For parser, use new op ref type, op list wrapper type, instead of ptrlist. * 2019-12-02: Move label and link_type fields to op ref type, and refactoring. Set version to v0.3.4. * 2019-12-03: Use mempool in parser for all parse result allocation. Increase version suffix to 'b'.