Allow `-` for stdout in path mapper (alecthomas#147)

More group formatting tweaks.

Add a bit of extra spacing if group description is provided.

See alecthomas#135.

Support a simplified `kong.Groups{<key>: <title>}` way of specifiying…

… groups.

See alecthomas#135.

Ensure values aren't nil before decoding.

When using resolvers, use last value only.

This fixes an issue where the value and all its hooks would
be applied for each resolver, making it difficult to compose multiple
config files.

Allow unsetting of FileContentFlag values.

Revert "Convert env management to a resolver."

This reverts commit fbe8d48.

Correctly parse all numeric types.

Fixes alecthomas#76.

Ensure "existingfile" doesn't choke on "-".