adding a .gitignore file

To be not confused by the auto generated autoreconf files putting these
into a .gitignore file.

.gitignore

@@ -0,0 +1,32 @@
+# .gitignore for libcoap
+
+# ignoring autogenerated files and directories by autoreconf
+INSTALL
+Makefile
+Makefile.in
+aclocal.m4
+ar-lib
+autom4te.cache/
+coap_config.h*
+compile
+config.*
+configure
+debian/
+depcomp
+install-sh
+libtool
+ltmain.sh
+m4/
+missing
+src/.deps/
+stamp-h1
+
+# ignoring more files generated by the configure script or the make actions
+.libs/
+src/.dirstamp
+src/.libs/
+libcoap*.la
+libcoap*.pc
+src/*.o
+src/*.lo
+