Auto merge of #363 - JustForFun88:fix_doc, r=Amanieu

Documentation fix due to latest changes in the crate.

Due to merged PR #357, #362 I think that we need to fix docummentation.

 Fixed broken links in `HashMap::raw_table` and `HashSet::raw_table`, as well as some typos and mistakes elsewhere (especially in `EntryRef::or_insert_with_key`).

To fix #349, I removed capacity comparisons in all places (except `drain` and `clear`),  however left the phrase "keeps the allocated memory for reuse", because although the `erase` method may not release the capacity, the subsequent `rehash_in_place` function definitely will release all.

Close #349.

Author: bors