Extract config file handlers into a separate file

We used custom_load_conf() to load the configuration file and
io_save_conf() to save configuration. Move these functions, including
all helpers, to a central location.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

.gitignore

@@ -5,7 +5,6 @@ Makefile.in
 Makefile.in.in
 Makevars
 aclocal.m4
-config.*
 configure
 depcomp
 install-sh
@@ -15,6 +14,8 @@ stamp-h1
 autom4te.cache/
 m4/
 
+./config.*
+
 doc/*.1
 doc/*.html
 doc/*.pdf