[Docs] STYLIZING.md

[Syphdias]

This aims to

• migrate styling docs from wiki to git
• update/correct
• simplify
• expand

This is is a work in progress, feel free to suggest how to tackle this

Problems that need to be tackled:

• [x] Make sure settings are set before sourcing/loading p9k
• [x] Getting a list of all stateful segments and their states -> see respective docs
• [x] Getting list of all icons and where they are used -> see respective docs
• [x] links to CHANGELOG and CODE_OF_CONDUCT.md?
• [x] bold
• [x] true color
• [x] check if all examples in styling are valid
• [x] better/easier structure
• [x] "quick start": P9K_<segment>[_<state>]_[BACKGROUND|FOREGROUND|BOLD|ICON[_BOLD|_COLOR]]
• [x] explain colors 1-16
• [x] unify "Icon" and "Visual Identifier" (now VIs are ICONs, Icons were refering to segment specific icons, dropping this section in favour if segment documentation)
• [x] check links in README.md

[Syphdias]

I think a lot of the general stuff could be replaced with a simple table. What do you thing, @dritter?

Option	Default	Effect
P9K_PROMPT_ON_NEWLINE	false	Display the prompt on the next line. Also checkout the sgement newline.
P9K_RPROMPT_ON_NEWLINE	false	Display RPROMPT on the same line as PROMPT if P9K_PROMPT_ON_NEWLINE=true
P9K_MULTILINE_FIRST_PROMPT_PREFIX_ICON	?	If the prompt is more than one line, this will be the prefix for the first line.
P9K_MULTILINE_NEWLINE_PROMPT_PREFIX_ICON	?	If the prompt is at least tree lines, this will be the prefix for all lines that are neither the first nor the last.
P9K_MULTILINE_LAST_PROMPT_PREFIX_ICON	?	If the prompt is more than one line, this will be the prefix for the last line.
P9K_PROMPT_ADD_NEWLINE	false	Adds a newline before displaying the prompt
P9K_PROMPT_ADD_NEWLINE_COUNT	1	Change the amound of newlines added if P9K_PROMPT_ADD_NEWLINE=true.
P9K_DISABLE_RPROMPT	false	Disables RPROMPT.
P9K_COLOR_SCHEME	unset	Set to light to invert default background and foreground color.
P9K_{LEFT,RIGHT}_SEGMENT_SEPARATOR_ICON	?	This is the separator between two segments of different color.
P9K_{LEFT,RIGHT}_SUBSEGMENT_SEPARATOR_ICON	?	This is the separator between two segments of the same color.
P9K_WHITESPACE_BETWEEN_{LEFT,RIGHT}_SEGMENTS		How much space there is between segment text and segment separator.

[Syphdias]

@onaforeignshore Thanks so much for the comments!

[Syphdias]

Oh, also: truecolor/24bit color #1262 - currently not merged...

[dritter]

Thx @Syphdias