Engine and test improvements

Implemented constant, leave, single line comment, and improved regression tests.

alpha.42.2.3: Merge pull request #12 from timbarnes/Development

Added nested do .. i .. loop functionality.
Added +! and ? variable words.
Added tests for nested do loops and variables.
Added printout of the loop / control stack in the stepper.

Alpha release: improved regression testing

Changes include:

1. More complete regression testing
2. Better test tools: run-regression, regression-results
3. Added documentation strings for built-in words, accessible via see <builtin>
4. Created macro for operands to automate stack underflow checks and pops

alpha.24.2.1

A few fixes and updated tests and test code.

alpha.2.1.24

Bugfixes. Reversed true and false!

tForth version 0.1

Initial release of tForth. This release is incomplete, and a work in progress. Documentation in the doc folder. You need to also download the corelib.fs file, which should be placed in ~/.tforth as noted in the documentation.