Lots of name changes

[WIP] rename plotting functions and improve their documentation (#62)

* renames

bit more concistent names:
```
recurrencetext, recurrencescatter, recurrenceplot
```
also exporting `recurrencescatter`, because I want to put this to the docs as well.

* different names and abit more detail in docstrings

* fix tests

* change all x to R in rqa docs 

for documentation purposes

* correct quotes indocstrings