Add "make style" directive to format source code

Makefile.am

@@ -1,4 +1,10 @@
 SUBDIRS = src
 
-#pkgconfigdir = $(libdir)/pkgconfig
-#pkgconfig_DATA = libnfc.pc
+style:
+	find . -name "*.[ch]" -exec perl -pi -e 's/[ \t]+$$//' {} \;
+	find . -name "*.[ch]" -exec astyle --formatted --mode=c --suffix=none \
+		--indent=spaces=2 --indent-switches --indent-preprocessor \
+		--keep-one-line-blocks --max-instatement-indent=60 \
+		--brackets=linux --pad-oper --unpad-paren --pad-header \
+		--align-pointer=name {} \;
+