Better modification API

The following discussion from !33 (merged) should be addressed:

• @jkuchar1 started a discussion: (+1 comment)

  Tak mě napadá, že vlastně můžeme podporovat stejné API jako u create. modify(test: 'xyz')... Follow up?

Souvisí s #8 (closed), #14.

Až to bude, dovedu si představit i $modifications = $row->modify(/* ... */);

mentioned in merge request !33 (merged)

mentioned in merge request !49

mentioned in merge request !50 (merged)

mentioned in commit 29b430c7

closed with merge request !50 (merged)