Added line prefixing option

[edam]

Added a line prefixing options, options.prefix, which prefixes all but the first line output.

E.g.

lua> t = { a = { b = 1 } }
lua> print( inspect( t, { newline = '', indent = '', prefix = ' ' ) )
{ a = { b = 1 } }
lua> print( '> '..inspect( t, { prefix = '> ' } )
> {
>   a = {
>     b = 1
>   }
> }

Also updated docs and tests

[coveralls]

Coverage remained the same at 99.294% when pulling 5a41302 on edam:add-padding into b611db6 on kikito:master.

[hishamhm]

This achieves the same result:

> t = { a = { b = 1 } }
> print( "> " .. inspect( t, { newline = '\n> ', } ) )
> {
>   a = {
>     b = 1
>   }
> }
> 

[kikito]

Closing because of the existing alternative (thanks for the PR though!)