process.c: move execve and execv parsers to a separate file

* execve.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* process.c: Move sys_execve, sys_execv, and related code to execve.c.
diff --git a/Makefile.am b/Makefile.am
index ce00548..c344338 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -30,6 +30,7 @@
 	count.c		\
 	desc.c		\
 	dirent.c	\
+	execve.c	\
 	fadvise.c	\
 	fallocate.c	\
 	fanotify.c	\