Bitcask FAQ section has malformed links. [JIRA: DOC-829]

http://docs.basho.com/riak/kv/2.2.0/setup/planning/backend/bitcask/#faq

```
[[Why does it seem that Bitcask merging is only triggered when a Riak node is restarted?|Developing on Riak FAQs#why-does-it-seem-that-bitc]]
[[If the size of key index exceeds the amount of memory, how does Bitcask handle it?|Operating Riak FAQs#if-the-size-of-key-index-e]]
```