Integrating Taler.

[stanisci]

This pull request aims to add Taler(.net) among the supported payment methods.

[codecov-io]

Codecov Report

Merging #158 into master will increase coverage by 0.54%.
The diff coverage is 86.76%.

@@            Coverage Diff             @@
##           master     #158      +/-   ##
==========================================
+ Coverage   79.59%   80.14%   +0.54%     
==========================================
  Files          27       29       +2     
  Lines        1642     1778     +136     
  Branches      191      209      +18     
==========================================
+ Hits         1307     1425     +118     
- Misses        231      243      +12     
- Partials      104      110       +6

Impacted Files	Coverage Δ
payments/taler/__init__.py	81.69% <81.69%> (ø)
payments/taler/amount.py	92.3% <92.3%> (ø)

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[WhyNotHugo]

This project was stale and unmaintained for quite some time.

I've been maintaining it for the past months. Are you still interested in getting this merged, or have you moved elsewhere?