Address issue #1 and change wording for Clap

src/bytecode.rs

@@ -63,7 +63,7 @@ pub fn from_bytecode(bytecode: &Vec<u8>) -> Result<(usize, Vec<Vec<Token>>), Str
 
     for (index, bytoken) in segment2.enumerate() {
         let token = try_err_fallthru!(Token::from_bytearray(&bytoken),
-                                          format!("Failed to convert from bytes to Token in chunk index {}: ", index));
+                                      format!("Failed to convert from bytes to Token in chunk index {}: ", index));
         if token.type_ == TokenType::KEYWORD {
             toks.push(vec![token]);
         } else {

src/main.rs

@@ -22,7 +22,7 @@ fn main() {
 	let clap_matches = App::new("Assembunny-plus")
 		.version("0.0.1")
 		.author("Michael P. <michael@mcmoo.org>")
-		.about("A C compiler and interpreter for Assembunny+, an ASM-like language extended from the Assembunny concept in Advent of Code 2016")
+		.about("A compiler, interpreter, and bytecode manager for Assembunny+, an ASM-like language extended from the Assembunny concept in Advent of Code 2016")
 		.arg(Arg::with_name("interpret")
 			.short("i")
 			.long("interpret")

src/parser.rs

@@ -300,6 +300,9 @@ pub fn to_tokens(line: &str, existing_regs: &mut Vec<String>) -> Result<Option<V
 
     // If keyword is "def", add the defined register to `existing_regs` because the existence of this register will be checked later
     if str_toks[0].to_lowercase() == "def" {
+        if existing_regs.contains(&str_toks[1].to_owned()) {
+            return Err(format!("def {}: Register name already exists", str_toks[1]));
+        }
         existing_regs.push(str_toks[1].to_owned());
     }