Add a token pattern to form symbols with complex names

[Necr0x0Der]

It might be useful to have a way to specify symbols with names including whitespaces and other symbols, e.g.

`2-LTR circle formation`

[vsbogd]

I would suggest allowing escape sequences in symbols (at the moment they are allowed only in strings) like following:

(= (foo $x) $x)

!(foo ab)    ;[ab]
!(foo a\ b)  ;[a b]
!(foo a b)   ;[(foo a b)]

Also this change should include fix for atom printing procedure to print atom using escaping sequence when whitespace is inside: a\ b.

[vsbogd]

I agree that both syntax forms make sense back quotes and escape sequences. Most important thing to me is that if we allow spaces inside symbols then we need modifying string representation of the symbols accordingly. Otherwise code of the program (foo `a b`) may be printed as (foo a b).