Use sortedcontainers rather than blist for faster, more pure-Python implementation

[Grant Jenks]

Hi, I noticed you're using the sortedlist and sorteddict implementations from the blist module in a few places:

1. https://github.com/citiususc/qrsdel/blob/master/qrsdel/qrsdel.py
2. https://github.com/citiususc/qrsdel/blob/master/qrsdel/utils/rame_douglas_peucker.py
3. https://github.com/citiususc/qrsdel/blob/master/error_measurements.py

Consider using the sortedcontainers module in place of blist. SortedContainers is a pure-Python implementation of SortedList, SortedDict, and SortedSet types that's actually faster than blist.

If you're interested, I'm happy to submit a pull request. Let me know.

[T. Teijeiro]

Hi Grant,

Thanks for your suggestion. I didn't know the sortedcontainers module, but it seems a better option for providing fast implementations of sorted collections, so I encourage you to replace the dependencies in the project and submit a pull request.

Regards

[Grant Jenks]

Pull request created at #2