Added option single_token_only and Updated README.md

[anandphulwani]

If we want the whole search query to be not split by spaces into words to generate tokens and want the whole search query to be just one token, we can set the single_token_only to true.

[coveralls]

Coverage decreased (-0.4%) to 93.069% when pulling 2683982 on anandphulwani:single-token-only-option into 97270b4 on brianreavis:master.