Allow digits in label names

Also, only allow a-zA-Z as the first character of label names.

examples/jmp_to_address_in_acc.mimasm

@@ -1,4 +1,4 @@
-IAR = technique-a
+IAR = technique-1
 
 ; This file demonstrates a few techniques for jumping to an address
 ; stored in the ACC.
@@ -9,15 +9,15 @@ tmp:              LIT 0
 
 ; Jumping by setting the RA and then returning
 100:
-technique-a:
-  LDC technique-b
+technique-1:
+  LDC technique-2
   STRA
   RET
 
 ; Jumping by writing a JMP instruction to a memory location and then
 ; jumping to that (aka. almost self-modifying code)
 200:
-technique-b:
+technique-2:
   LDC end
   OR jump-instruction
   STV tmp

src/Mima/Assembler/Parser.hs

@@ -39,11 +39,8 @@ incrementCurrentPos = do
   put s{sCurrentPos = succ $ sCurrentPos s}
 
 parseInstructions' :: SParser ()
-parseInstructions' = sepBy parseInstruction' incrementCurrentPos >> lift (eof <|> fail atMaxAddress)
+parseInstructions' = sepBy parseInstruction' incrementCurrentPos >> lift eof
   where
-    atMaxAddress = "already at maximum address (" ++ show (maxBound :: MimaAddress)
-                   ++ ") - can't go any further"
-
     parseInstruction' :: SParser ()
     parseInstruction' = do
       s <- get

src/Mima/Assembler/Parser/Label.hs

@@ -10,6 +10,7 @@ module Mima.Assembler.Parser.Label
   , resolveAddress
   ) where
 
+import           Data.Char
 import qualified Data.Map as Map
 import qualified Data.Text as T
 import           Text.Megaparsec
@@ -33,8 +34,10 @@ mimaLabel = lexeme mimaLabel'
 
 mimaLabel' :: Parser MimaLabel
 mimaLabel' = label "label" $ do
-  name <- takeWhile1P Nothing (\c -> isAlphabet c || isConnecting c)
+  firstChar  <- satisfy isAlphabet
+  otherChars <- takeWhileP Nothing (\c -> isAlphabet c || isConnecting c || isDigit c)
   offset <- getOffset
+  let name = T.singleton firstChar <> otherChars
   pure MimaLabel{lName = name, lOffset = offset}
 
 failAtLabel :: MimaLabel -> String -> Parser a