adds movement for start of word, regardless of stop characters

[rwese]

regarding #195 #1954 (comment)

Sample test/with-characters that cause stopps
                    -(cursor)
       -(after hitting MoveBackwardWordStart)

otherwise would need 2 MoveBackwardWord actions.

[rwese]

it's missing documentation, I just wanted to get some feedback if this is the proper way to implement the new movement.

[bew]

About naming, I think MoveBackwardWordStart & MoveBackwardWord are not different enough (I thought they were the same at the beginning).
Maybe rename to MoveBackwardWORD (but that breaks camelcase-ing..), or MoveBackwardBigWord ?

Also, instead of basically re-implementing move_backward_one_word with slightly different behavior, I think it would be better to refactor the function if possible, for example to make it accept a predicate function for the separator to stop at 🤔

[rwese]

Naming is always hard, I thought it would fit well with "moveForwardEnd" > "BackwardStart".

In terms of code, I took the easy way, not wanting to have to deal with breaking changes and refactoring. But I can give it a refactor, need to look into the test-cases.