Adding config file parsing implementation

Parameters from config file will be added at --cfg options location to
be processed

Config file example:
 #ignore comment
 ext-partition   : 1 #ignore as well
 codec           : av1
 psnr            : ON

Note(s):
    - Config file is a simple text file
    - Comment starts with hash(#)
      Can be full line or part of the line, after hash(#) details are
ignored
    - Format: field : value
      colon(:) as delimeter, otherwise full line will be ignored
      Space(s) and tab(s) can be used, not inside field
    - long names for field are prefered
       existing --long_name option format
    - "no value" fields should contain ON as value

Example of usage:
    aomenc --cfg=some.cfg src_filename

Configurations support matrix:
enable-ext-partition         : done
enable-loop-restoration      : wip
enable-deblocking            : wip
...

Change-Id: Iad867c5d2da64271cdafa825c89f7d6444582f61
diff --git a/args.h b/args.h
index c3427bc..d129736 100644
--- a/args.h
+++ b/args.h
@@ -48,6 +48,9 @@
 
 struct arg arg_init(char **argv);
 int arg_match(struct arg *arg_, const struct arg_def *def, char **argv);
+char *ignore_front_spaces(const char *str);
+void ignore_end_spaces(char *str);
+int arg_cfg(int *argc, char ***argv, const char *file);
 const char *arg_next(struct arg *arg);
 void arg_show_usage(FILE *fp, const struct arg_def *const *defs);
 char **argv_dup(int argc, const char **argv);