Xapian bridge now supports offset parameter

This adds support for 'offset' parameter in the xapian bridge.
The offset specifies from where in the result set to start
returning results. We now also return totalResults and offset
as part of the response from the xapian bridge.
Merge pull request #22 from endlessm/sdk/1802

Xapian bridge now supports offset parameter
Check if offset and limit parameters are numbers

Previously, we were not converting the limit and offset
parameters to integer types, which meant that a) there
was no verification that they were valid numbers and b)
they were sent back as type string to the client, which
was wrong. This ensures that they are converted to valid
numbers.
Merge pull request #23 from endlessm/sdk/1802

Check if offset and limit parameters are numbers
Added cutoff option to queries

Calls to /:index/query now support a cutoff querystring parameter. This accepts
a floating point number which will be used in Xapian's Enquire::set_cutoff method
for setting the percentage cutoff

[endlessm/eos-sdk#1819]
Merge pull request #24 from endlessm/sdk/1819

Added cutoff option to queries