Allow splitting string literals over multiple lines

[axic]

Many languages support splitting string literals overs multiple lines. Some require a special token between them.

I'd propose that parsing (hex) string literals would allow " as the next token and start concatenating the literals. Any whitespace, including new lines, would be allowed between the two " tokens.

E.g. bytes tmp = hex"00112233" "44556677"; would be equivalent to hex"0011223344556677".

[chriseth]

Sounds good! I would support that for all kinds of strings.