Create parsers with empty source file name
Create parsers with empty source file name

(instead of "file")

Due to changes in rustc, "file" was added to the crate's dep-info
output, which caused cargo to recompile any crate that uses rust-peg
unconditionally.

loganmhb/rust-peg,daramos/rust-peg,kevinmehall/rust-peg,kevinmehall/rust-peg,loganmhb/rust-peg,tempbottle/rust-peg,a-wortman/rust-peg,a-wortman/rust-peg,tempbottle/rust-peg,jsgf/rust-peg,daramos/rust-peg,jsgf/rust-peg