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 "-".

Allow Run() on arbitrary nodes.

This is useful for dynamically running commands.

Convert env management to a resolver.

This ensures that hooks correctly detect when values are set via
environment variables. Fixes alecthomas#73.

Expand variables in config paths.

Allow binds to be provided by a function.

This is useful for situations where the initialisation of some object
should be deferred, eg. when there are distinct "setup" and "use" phases
to a tools lifecycle.

Correctly support encoding.{TextUnmarshaler,BinaryUnmarsheler}