Redesign speed-type-wordlist-transform to be used for all-commands

[lordnik22]

With speed-type-pandoc depending on the website the user is converting he might want to filter certain annoying patterns. These patterns are specific to the structure of the website and the pandoc-conversion (which is a best effort conversion). It can get very specific, so the user knows best what patterns he might want to filter. Applying a general rule would be a overkill for other users.

An example what a user might want to filter are references on wikipedia-pages: ([3]).

The mechanism should also allow to skip whole sections and start where it get's interesting for the user.

For example wikipedia-pages come often we a big language-list at the start which needs to be skipped before the content starts. There is currently only the workaround to store manually an entry in the speed-type-statistic-filename which sets speed-type--continue-at-point to the desired continue-point.

Considering the above the new procedure should look something like: pick -> put-text-property -> filter -> replace -> trim -> pick -> put-text-property -> filter -> replace -> trim -> pick -> ... until enough typing-material is collected or end of buffer is reached.

The procedure and existing function (step by step):

1. pick = speed-type--pick-continue-text-bounds
2. put-text-property = speed-type--put-text-property-orig-pos
3. filter -> [To be implemented]
4. replace = speed-type--replace-map-adjust-properties
5. Repeat
   Finally: trim = string-trim or speed-type--trim

This procedure should be used for all commands. If the custom-variable is nil the filter-step should be skipped (it should be behave as is). Therefore it's an opt-in feature. The custom filters should be formulated general enough to work for all commands (the filter-function should a some context-arguments (e.g. identifies the used command). So the individual custom-function decides if it filters something or not depending on the context.

It should be documented in detail how these filter-functions are expected and which context-arguments are provided. It should show some example cases for the context-arguments, when to use them and when to ignore them.

The content-buffer should stay untouched so continue-at-point doesn't get corrupted.

[lordnik22]

This new design could result in a rework of speed-type-stop-words or speed-type-downcase.

[lordnik22]

basically add a speed-type-pick-content-hook which is triggered on "setup" and "add-words-on-error"