Add function to add bits from array to bitvec

Add function which adds specified number of bits from each element of
array to the bit vector prefixing each addition with one and finishing
entire sequence with adding 0. This is very common patter for various
repetitive data structures described with CSN.1 in 3GPP standards.

Corresponding test vectors and doxygen headers are added too.
diff --git a/include/osmocom/core/bitvec.h b/include/osmocom/core/bitvec.h
index 5314cf2..c3c1153 100644
--- a/include/osmocom/core/bitvec.h
+++ b/include/osmocom/core/bitvec.h
@@ -91,5 +91,8 @@
 unsigned bitvec_rl(const struct bitvec *bv, bool b);
 void bitvec_shiftl(struct bitvec *bv, unsigned int n);
 int16_t bitvec_get_int16_msb(const struct bitvec *bv, unsigned int num_bits);
+unsigned int bitvec_add_array(struct bitvec *bv, const uint32_t *array,
+			      unsigned int array_len, bool dry_run,
+			      unsigned int num_bits);
 
 /*! @} */