Add shebang support

[Rerumu]

Closes #106
If a script starts with the characters #! then the first line is skipped.

[LoganDark]

I actually think this should be in the CLI. Shebang is not a part of the Luau syntax. Files starting with one should be interpreted as if the source code starts after the shebang.

Roblox scripts don't have shebangs, loadstrings don't have shebangs, etc. shebangs are really only for loading from files.

[Rerumu]

Roblox scripts don't have shebangs, loadstrings don't have shebangs, etc. shebangs are really only for loading from files.

Makes sense. I've gone ahead and moved the check to readFile which is used by the CLI to read source files. I've also made it skip if the first character is # without checking the second character, since it seems that's what vanilla does too.

[zeux]

Thanks! And sorry it took so long :) I'll change the PR a bit to detect #! pattern instead of # to make sure we're detecting the shebang instead of a comment that accidentally uses the wrong syntax and merge this.