Remove TestClass from test_formatting_api
Make populate work with no args...

for StringWithFormatting and StringComponentSpec. This makes interactive
testing/exploration easier.
Update populate docstring
Add beginnings of colour picker example...

Note that we use draw at the bottom right now because I was running it and saw
how bad the performance was! Currently using this example to profile the code
and improve performance.
WIP remove sanitisation code which is making stuff slow...
Make ABCUIElement more flexible with regards to drawing 'populatable' things
WIP cache str for speed
Try alternate StringWithFormatting data structure
WIP Making new StringComponent which inherits directly from string
WIP Fix strip method of StringWithFormatting
WIP Refactor string component stuff (again)

 - StringWithFormatting now only composed of singly-formatted StringComponent
   objects
 - Redo most formatting API tests
 - Hopefully will increase draw speed
Add repr to ParameterizingFormatPlaceholder
Fix addition in the formatting api...

having changed the data structures underneath, all this was broken! It's still
rather messy and needs cleaning up, but it's more-or-less working now.
Remove unnecessary str caching in StringWithFormatting...

When I benchmarked it, it actually now seems to make it slower!
Remove unused StringComponentSpec and EscapeSequenceStack classes
Remove unneccessary casting to StringWithFormatting in chunk method...

StringComponents are str-like, so there's no point.
FIXUP removal of StringComponentSpec
Fix textwrap test
Add addition test for StringComponent
Fix default formatting to work with new StringComponent stuff