Edi Reader does not respect X12 advised control characters

In all known EDI formats there are default control characters these are documented in the default `EdiGrammar` presets.
- `EdiGrammar.NewEdiFact()`
- `EdiGrammar.NewX12()`
- `EdiGrammar.NewTradacoms()`

Now in the EdiFact and X12 cases there is a way for the transmitter (he who sends the edi transmission)
to advise differently for each of the control characters.

Control characters are considered to be the segment, element & component seperators plus the escape character.

In X12 the current implementation completely ignores them.

Start by comparing the default EdiGrammar.NewEdiFact(), EdiGrammar.NewX12(), and EdiGrammar.NewTradacoms() presets with the X12 reader implementation. Trace how advised segment, element, component, and escape characters are handled, then verify that X12 transmissions using non-default control characters are parsed correctly.

Written by the indexing model from the issue text.