Enhancements?

[mathew-kurian]

Thank you for this great library!!! I have forked the library and added a few more features. So, if you would like to merge these changes please let me know and I can clean it up and add test cases. If there any issues, please me know. The features added are as follows:

Querying

Support for multiple subsequent add/subtract calls.

 RangeA.subtract(RangeB).subtract(RangeC).add(RangeD).by(...)

Query String

Additionally, moment.range has been modified to also support with a range query string inputs which will be converted to a DateRange. Examples of this are as follows:

1. (2009>>2012)
2. (2009>>2012)(^2008-2010)
3. (January 1, 2012>>2015)

Subtraction Boundary

You can say whether you want to include/exclude the boundary dates during subtraction.

// 1 second offset from left/right of range
RangeA.subtract(RangeB).subtract(RangeC, 1, 's') 

Note: This can be done by the user quite easily, but I figured it would be awesome if the library supported it.

[gf3]

Sorry for the delay in getting back to you (been crazy busy). I'm definitely interested in these updates. If you provide a PR with docs & tests I'd be more than happy to merge it in and add you to the contributors. Thank you!