Added generic key-value parser for parsing command line parameters.
Merge pull request #75 from tasdomas/key-values

Added generic key-value parser for parsing command line parameters.
jsonhttp: safer handlers
Merge pull request #76 from rogpeppe/004-safer-jsonhttp

jsonhttp: safer handlers
Move all the interfaces into one file.
Add missing doc comments to the interfaces.
Factor out Doc, DocStorage, and MetadataDocStorage types.
Add fake storage implementations for testing.
Move the simple implementations into their own package.
Clean up the wrapper tests.
simple -> basic.
Init docs in NewDocStorage().
Include the filename in error messages.
Add a missing doc comment.
Add more detail to a doc comment.
Drop unnecessary comment.
Drop unnecessary parentheses.
Fix gocheck imports.
Fix up a couple doc comments.
Move interface checks into tests.