Add a simple option parser.

The option parser takes argc, argv, an array of struct option
and a usage string.  Each of the struct option elements in the array
describes a valid option, its type and a pointer to the location where the
value is written.  The entry point is parse_options(), which scans through
the given argv, and matches each option there against the list of valid
options.  During the scan, argv is rewritten to only contain the
non-option command line arguments and the number of these is returned.

Aggregation of single switches is allowed:
  -rC0 is the same as -r -C 0 (supposing that -C wants an arg).

Every long option automatically support the option with the same name,
prefixed with 'no-' to unset the switch. It assumes that initial value for
strings are "NULL" and for integers is "0".

Long options are supported either with '=' or without:
  --some-option=foo is the same as --some-option foo

Acked-by: Kristian Høgsberg <krh@redhat.com>
Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

parse-options.h

@@ -0,0 +1,35 @@
+#ifndef PARSE_OPTIONS_H
+#define PARSE_OPTIONS_H
+
+enum parse_opt_type {
+	OPTION_END,
+	OPTION_BOOLEAN,
+	OPTION_STRING,
+	OPTION_INTEGER,
+};
+
+enum parse_opt_flags {
+	PARSE_OPT_KEEP_DASHDASH = 1,
+};
+
+struct option {
+	enum parse_opt_type type;
+	int short_name;
+	const char *long_name;
+	void *value;
+};
+
+#define OPT_END()                   { OPTION_END }
+#define OPT_BOOLEAN(s, l, v, h)     { OPTION_BOOLEAN, (s), (l), (v) }
+#define OPT_INTEGER(s, l, v, h)     { OPTION_INTEGER, (s), (l), (v) }
+#define OPT_STRING(s, l, v, a, h)   { OPTION_STRING,  (s), (l), (v) }
+
+/* parse_options() will filter out the processed options and leave the
+ * non-option argments in argv[].
+ * Returns the number of arguments left in argv[].
+ */
+extern int parse_options(int argc, const char **argv,
+                         const struct option *options,
+                         const char *usagestr, int flags);
+
+#endif