[Language] Allow breaking long lines using `\`

[rturrado]

For example, the code below should be a valid example:

version \
3

This is not supported by the lexer at the moment. \ is not a recognized token. I don't think it should be a big change. I'm sure there are already solutions out there for this issue. The lexer should say something like: OK, whenever you find the token \ followed by the token NEW_LINE, update the line counter, but delete the new line. Something like that.