Feature/python improvements

[jefferis]

Use miniconda unless own python is specified

• should also help if miniconda has been installed by reticulate but not added to the path

[codecov[bot]]

Codecov Report

Merging #171 (16bb345) into master (323fd06) will decrease coverage by 0.32%. The diff coverage is 37.66%.

:exclamation: Current head 16bb345 differs from pull request most recent head aebb091. Consider uploading reports for the commit aebb091 to get more accurate results

@@            Coverage Diff             @@
##           master     #171      +/-   ##
==========================================
- Coverage   52.91%   52.59%   -0.32%     
==========================================
  Files          36       36              
  Lines        4347     4407      +60     
==========================================
+ Hits         2300     2318      +18     
- Misses       2047     2089      +42     

Impacted Files	Coverage Δ
R/zzz.R	11.76% <0.00%> (-0.74%)	:arrow_down:
R/utils.R	48.45% <38.15%> (-3.22%)	:arrow_down:

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