Docs: make the welcome page more obvious

Closes #26.

(cherry picked from commit bb823d1)
Add `smartcn_word` & `smartcn_sentence` back for backwards compatibility

In f4d0d27 the deprecated `smartcn_sentence` tokenizer and deprecated
`smartcn_word` token filter were removed as the new all in one
`smartcn_tokenizer` should be used instead. However for those with pre-existing
indices with mappings that reference the deprecated tokenizer and token filter
this changes causes indexing and search errors.

This change preserves the `smartcn_sentence` tokenizer name and aliases it to
the new `smartcn_tokenizer`. The change set also reintroduces a `smartcn_word`
token filter that is a noop filter. The result of these changes should allow
elasticsearch instances with the existing deprecated mappings to upgrade and
take advantage of the new tokenizer in lucene.