Update code style

Limit source code to 80 chars, and declare functions return type and
modifiers on a separate line.

This allows to avoid very long lines, and all function names are
aligned.

(We do this on VLC, and I like it.)

app/src/lock_util.c

@@ -4,28 +4,32 @@
 
 #include "log.h"
 
-void mutex_lock(SDL_mutex *mutex) {
+void
+mutex_lock(SDL_mutex *mutex) {
     if (SDL_LockMutex(mutex)) {
         LOGC("Could not lock mutex");
         abort();
     }
 }
 
-void mutex_unlock(SDL_mutex *mutex) {
+void
+mutex_unlock(SDL_mutex *mutex) {
     if (SDL_UnlockMutex(mutex)) {
         LOGC("Could not unlock mutex");
         abort();
     }
 }
 
-void cond_wait(SDL_cond *cond, SDL_mutex *mutex) {
+void
+cond_wait(SDL_cond *cond, SDL_mutex *mutex) {
     if (SDL_CondWait(cond, mutex)) {
         LOGC("Could not wait on condition");
         abort();
     }
 }
 
-void cond_signal(SDL_cond *cond) {
+void
+cond_signal(SDL_cond *cond) {
     if (SDL_CondSignal(cond)) {
         LOGC("Could not signal a condition");
         abort();