Change dec2bitarray to a faster implementation

The current and previous implementations of dec2bitarray are a huge chunk of time of the simulation.
This implementation is the fastest that I have found, comparing with the previously used ones.
Is based on this SO answer: https://stackoverflow.com/a/30227161

Author: eSoares

commpy/utilities.py

@@ -46,9 +46,15 @@ def dec2bitarray(in_number, bit_width):
         Array containing the binary representation of all the input decimal(s).
 
     """
-
-    binary_words = vectorized_binary_repr(np.array(in_number, ndmin=1), bit_width)
-    return np.fromiter(it.chain.from_iterable(binary_words), dtype=np.int8)
+    result = np.zeros(size, 'int')
+    i = 1
+    pox = 0
+    while i <= number:
+        if i & number:
+            result[size - pox - 1] = 1
+        i <<= 1
+        pox += 1
+    return result
 
 
 def bitarray2dec(in_bitarray):