feat: Add token definitions and lexer logic.

This commit adds the `Token` and `TokenKind` definitions in `src/token.rs`,
in `src/lexer.rs` I've added the `Lexer` logic.

src/cli.rs

@@ -16,12 +16,12 @@ pub fn print_help() {
     println!();
     println!("{}", "OPTIONS:".bold().yellow());
     println!(
-        "  {}, {}    Print this help message",
+        "  {}, {}      Print this help message",
         "-h".bold(),
         "--help".bold()
     );
     println!(
-        "  {}, {}  Print version information",
+        "  {}, {}   Print version information",
         "-V".bold(),
         "--version".bold()
     );
@@ -34,7 +34,7 @@ pub fn print_help() {
         "-c".bold()
     );
     println!(
-        "  {} {}      Write output to <file>",
+        "  {} {}       Write output to <file>",
         "-o".bold(),
         "<file>".bold(),
     );
@@ -42,7 +42,7 @@ pub fn print_help() {
     println!();
     println!("{}", "ARGS:".bold().yellow());
     println!(
-        "  {}    One or more Flux source files to compile",
+        "  {}    One or more source files to compile",
         "<file>".bold(),
     );
 }