More strict typing of some methods

[mateuszbaran]

I've put some bounds on types in a few methods. We may also need a few more methods for basis-related function forwarding but I'll think a bit more how to introduce them.

[kellertuer]

Looks good.

[codecov[bot]]

Codecov Report

Merging #97 (3281874) into master (b598a13) will decrease coverage by 0.04%. The diff coverage is 100.00%.

:exclamation: Current head 3281874 differs from pull request most recent head c7e1fa8. Consider uploading reports for the commit c7e1fa8 to get more accurate results

@@            Coverage Diff             @@
##           master      #97      +/-   ##
==========================================
- Coverage   99.80%   99.75%   -0.05%     
==========================================
  Files          17       17              
  Lines        2046     2043       -3     
==========================================
- Hits         2042     2038       -4     
- Misses          4        5       +1     

Impacted Files	Coverage Δ
src/point_vector_fallbacks.jl	100.00% <100.00%> (ø)
src/retractions.jl	100.00% <100.00%> (ø)
src/vector_transport.jl	100.00% <100.00%> (ø)
src/ManifoldsBase.jl	97.63% <0.00%> (-1.58%)	:arrow_down:
src/ValidationManifold.jl	99.48% <0.00%> (-0.52%)	:arrow_down:
src/numbers.jl	100.00% <0.00%> (ø)
src/PowerManifold.jl	99.77% <0.00%> (+0.44%)	:arrow_up:

:mega: Codecov can now indicate which changes are the most critical in Pull Requests. Learn more

[mateuszbaran]

I think this is ready now.