doxygen: enable AUTOBRIEF, drop \brief

Especially for short descriptions, it is annoying to have to type \brief for
every single API doc.

Drop all \brief and enable the AUTOBRIEF feature of doxygen, which always takes
the first sentence of an API doc as the brief description.

Change-Id: I11a8a821b065a128108641a2a63fb5a2b1916e87
diff --git a/src/bitcomp.c b/src/bitcomp.c
index 9c01246..acf165e 100644
--- a/src/bitcomp.c
+++ b/src/bitcomp.c
@@ -25,7 +25,7 @@
  */
 
 /*! \file bitcomp.c
- *  \brief Osmocom bit compression routines
+ *  Osmocom bit compression routines
  */
 
 #include <stdint.h>
@@ -222,7 +222,7 @@
 	 }
 };
 
-/*! \brief Make-up codes for a given length
+/*! Make-up codes for a given length
  *
  *  \return Return proper make-up code word for an uninterrupted
  *  sequence of b bits of length len according to modified ITU-T T.4
@@ -307,7 +307,7 @@
 	return bitvec_set_uint(bv, t4_term[b][len], t4_term_length[b][len]);
 }
 
-/*! \brief encode bit vector in-place using T4 encoding
+/*! encode bit vector in-place using T4 encoding
  *  Assumes MSB first encoding.
  *  \param[in] bv bit vector to be encoded
  *  \return color code (if the encoding started with 0 or 1) or -1 on