Improve documentation
Introduce AssemblingError class
Merge branch 'master' into 47-strict-assembling
Merge branch 'master' into 47-strict-assembling
Add tests for #47 (failing ATM)
Merge branch 'master' into 47-strict-assembling

Conflicts:
	argh/assembling.py
Normalize hyphen/underscore when comparing a declared arg with function signature
Require an arg to be either positional or optional
Refactor assembling, use OrderedDict
Merge pull request #54 from neithere/47-strict-assembling

Stricter comparison of inferred+declared arguments on assembling