strip leading/trailing space before tokenisation

prevents stray empty strings from entering the index
implement sorted set indexOf as a binary search

results in vastly improved performance since we know the set elements
are sorted
expose stop words list as a sorted set

allows easy addition of extra stop words if required
using sorted set also results in greater performance
add JSON.stringify support

serialises the index and all its stores
add load to index

loads a previously serialised index
implement serialisation of the pipeline

pipeline functions need to be registerd if they are to be serialised
the pipeline will issue warnings about using unregistered pipeline functions
add an integration test covering serialisation
pre-build the example index
serialise documentation
build version 0.3.0
Ignore when removing a non-existent document on the index
Missing comma o test making variable a global
Merge pull request #24 from ShareIt-project/master

Ignore when removing a non-existent document on the index
build version 0.3.1
fixes #27
don't try and calculate tf for empty fields

was causing issues when adding a document with an empty field, 0 / 0 would give a NaN which would end up as the tf, and then as the documents score against a query
Merge pull request #31 from olivernn/pr/28

Fix bug when indexing a document with empty fields
build version 0.3.2
Extract warning logging into a dedicated function

Should work in browser, Node, and Web Worker environments.
add augment to the test suite