ENH: Reexport functions from modules

[bifbof]

closes #546
Changed how we export and import functions.
This makes the module paths clearer and additionally all links in the documentation work now as well.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1a93537) 93.04% compared to head (8bddf52) 93.10%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #567      +/-   ##
==========================================
+ Coverage   93.04%   93.10%   +0.06%     
==========================================
  Files          33       33              
  Lines        2069     2088      +19     
  Branches      372      373       +1     
==========================================
+ Hits         1925     1944      +19     
  Misses        130      130              
  Partials       14       14              

Files	Coverage Δ
trackintel/analysis/location_identification.py	99.09% <ø> (ø)
trackintel/analysis/modal_split.py	100.00% <100.00%> (ø)
trackintel/geogr/__init__.py	100.00% <100.00%> (ø)
trackintel/io/dataset_reader.py	46.90% <ø> (ø)
trackintel/io/file.py	100.00% <ø> (ø)
trackintel/model/locations.py	100.00% <100.00%> (ø)
trackintel/model/positionfixes.py	100.00% <100.00%> (ø)
trackintel/model/staypoints.py	100.00% <100.00%> (ø)
trackintel/model/tours.py	100.00% <100.00%> (ø)
trackintel/model/triplegs.py	100.00% <100.00%> (ø)
... and 6 more

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[hongyeehh]

Thanks for the detailed changes. It is great that the links in the docs are now working!