Improve string/interpolation formatting (#1491)

- The '#' component for type 's' now escapes the string characters
- The '#' component for type 'f' now prints a precision suffix
- The new 'q' component specifies a precision value

test/asm/string-formatting.asm

@@ -3,11 +3,12 @@ def m equ -42
 def f equ -123.0456
 def pi equ 3.14159
 def s equs "hello"
+def t equs "\"\\t\" is '\t'"
 
 	println "<{ -6d:n}> <{+06u:n}> <{5x:n}> <{#16b:n}>"
 	println "<{u:m}> <{+3d:m}> <{#016o:m}>"
 	println "<{f:pi}> <{06.f:f}> <{.10f:f}>"
-	println "<{#-10s:s}> <{10s:s}>"
+	println "\"{#-20s:t}\", \"{#20s:t}\", \"{20s:t}\""
 
 macro foo
 	println "\1 <{\1}>"