py-boltons: added version 20.2.0

Boltons is a set of pure-Python utilities in the same spirit as - and yet
conspicuously missing from - the standard library, including:

* Atomic file saving, bolted on with fileutils
* A highly-optimized OrderedMultiDict, in dictutils
* Two types of PriorityQueue, in queueutils
* Chunked and windowed iteration, in iterutils
* A full-featured TracebackInfo type, for representing stack traces, in tbutils
* A lightweight UTC timezone available in timeutils.
* Recursive mapping for nested data transforms, with remap

(adam)