(doc) Update PoolManager documentation

Update all documentation for `AutoNetwork::PoolManager` and remove the
`@api private` flag. Also add examples and descriptions of historical poolfile
serialization formats.
(doc) Mark methods and classes added in 1.0.0

Added `@since 1.0.0` to objects added in the 1.0.0 release.
(doc) Use YARD reference tags for PoolManager

The PoolManager class proxies a lot of methods from the Pool class. Use RDoc
reference tags to copy over the docstrings for these methods.