Adds SpecError and subclasses.

- Switch to using SpecError instead of err
- added support for printing the stacktrace in the base reporter.
Adds stacktrace spec.

Only runs if --tag stacktrace is specified.
Adds stacktrace printing to spec_reporter.
Adds stacktrace to dotmatrix reporter.
Adds stacktrace to tap reporter.
Adds stacktrace to min reporter
Adds stacktrace to dotmatrix reporter.
Merges branch 'feature/add-stacktrace' into develop

Closes #9

- to_throw and to_not_throw matchers will need bigger refactoring
- Possible suggestion, QUnit style, early to_throw that tags a spec like caught_exception
- At the expectation layer, check against this, etc.