Add ContT.liftF and ContT.liftK

[lavrov]

Closes #3271

[codecov-io]

Codecov Report

Merging #3274 into master will increase coverage by 0.32%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #3274      +/-   ##
=========================================
+ Coverage   93.08%   93.4%   +0.32%     
=========================================
  Files         376     372       -4     
  Lines        7428    7243     -185     
  Branches      196     181      -15     
=========================================
- Hits         6914    6765     -149     
+ Misses        514     478      -36

Flag	Coverage Δ
#scala_version_212	93.4% <100%> (-0.02%)	⬇️
#scala_version_213	?

Impacted Files	Coverage Δ
core/src/main/scala/cats/data/ContT.scala	100% <100%> (ø)	⬆️
...in/scala/cats/data/AbstractNonEmptyInstances.scala	96.55% <0%> (-3.45%)	⬇️
core/src/main/scala/cats/instances/option.scala	96.61% <0%> (-1.7%)	⬇️
...e/src/main/scala-2.13+/cats/data/ZipLazyList.scala
...src/main/scala-2.13+/cats/instances/lazyList.scala
....13+/cats/kernel/instances/LazyListInstances.scala
.../main/scala-2.13+/cats/data/NonEmptyLazyList.scala

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 93ebced...76bb641. Read the comment docs.

[LukaJCB]

This looks great, thank you! :)