Add overlap measure

[amadanmath]

One obstacle to implementing Overlap measure is the fact that the original implementation gives max size for that measure as INT_MAX.

To solve this, one can only restrict this at search time.

There may also be a possibility to implement the max size for mongo, however I've never worked with it and I don't dare touch it without even having it installed. :)

[icfly2]

HI, i'm looking into forking this and making a new module and repo, are you ok with me just adding the measure there?

[icfly2]

This is available in simstring which is a fork of this which is being maintained (for now)