Escape function for texts

[muesli]

When trying to display texts like [foobar] (as an actual text, not a color definition), a convenient little escape function would be handy, otherwise those texts are incorrectly interpreted as a color-markup.

[rivo]

Yeah, I want to add this. Not just for strings but also for io.Writer's so you can use it in the TextView primitive as well.

[rivo]

Btw, this also affects #91 so I will probably do this after introducing background colors.

[KingRikkie]

Please make it handle Umlauts äüö and brackets ( ) correctly. The current workaround with a strings.NewReplacer("]", "[]") fails when there are any of said chars inside the square brackets as tview will ignore the brackets then leading to something like this in viewport

string with [Ümlauts] in brackets -> string with [Ümlauts[] in brackets
string with [bra(kets] in brackets -> string with [bra(kets[] in brackets

[rivo]

The package now has an escape function. See Escape() for details.