Add Random Survival Forest

[sebp]

No description provided.

[codecov-io]

Codecov Report

Merging #90 into master will increase coverage by 0.11%.
The diff coverage is 99.54%.

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
+ Coverage   98.05%   98.16%   +0.11%     
==========================================
  Files          33       36       +3     
  Lines        2668     2886     +218     
  Branches      403      439      +36     
==========================================
+ Hits         2616     2833     +217     
  Misses         28       28              
- Partials       24       25       +1

Impacted Files	Coverage Δ
sksurv/ensemble/forest.py	100% <100%> (ø)
sksurv/ensemble/__init__.py	100% <100%> (ø)	⬆️
sksurv/tree/__init__.py	100% <100%> (ø)
sksurv/tree/tree.py	99.23% <99.23%> (ø)

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