Add the Copier type (#8)

* Checkpoint.

* Make Copy() optional; add Copier, remove ValueType.

When pulling a default parameter value out of a Param via type assert…

…ion, try all valid types. Fixes #4. (#5)

Adjust to limitations of Go's cross-reference markdown.

Permit variadic functions and flag.Value-typed parameters (#3)

* Checkpoint.

* Doc.

* Add support for flag.Value-typed parameters.

* Doc tweaks. Improve TestPrefix.

* Add missing file value_test.go. Add cross-reference syntax to godoc.

* Fix Readme links.

Check and external subcommands (#2)

Fix a documentation bug.

V2 of the API: better help, plus positional parameter parsing (#1)

* Draft of v2 API.

* Add Subcmd.Usage and a test.

* WIP: positional parameters.

* Checkpoint.

* Revise usage and error handling, add tests.

* More test coverage.

* Reduce cyclomatic complexity. Add godoc. Resolve golint warnings.

* s/Long/Detail/. Add more tests. Remove unused errors.

* Add default-value handling for optional positional args, and another test.

* Update doc and examples. Correctly handle flags mixed with positional params in a Params slice.

Fix a bug with zero-ary subcommands and add a regression test.

Add coveralls.io coverage and badge.

Awesome Go feedback: add test coverage; reduce cyclomatic complexity;…

… add usage example to Readme.