Allow tab character after backslash line continuation

Author: Rangi42

src/asm/lexer.cpp

@@ -1373,6 +1373,7 @@ static std::string readString(bool raw) {
 
 			// Line continuation
 			case ' ':
+			case '\t':
 			case '\r':
 			case '\n':
 				discardLineContinuation();
@@ -1505,6 +1506,7 @@ static void appendStringLiteral(std::string &str, bool raw) {
 
 			// Line continuation
 			case ' ':
+			case '\t':
 			case '\r':
 			case '\n':
 				discardLineContinuation();
@@ -1982,6 +1984,7 @@ static Token yylex_RAW() {
 				break;
 
 			case ' ':
+			case '\t':
 			case '\r':
 			case '\n':
 				discardLineContinuation();

test/asm/line-continuation-string.asm

@@ -1,3 +1,3 @@
 println "Line \  ; this comment is ignored
-continuations\   ; so is this one
+continuations\	; so is this one
  work!"          ; =)