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/av1/av1_cx_iface.c b/av1/av1_cx_iface.c
index 024926f..3304634 100644
--- a/av1/av1_cx_iface.c
+++ b/av1/av1_cx_iface.c
@@ -540,6 +540,7 @@
 
 #endif
   oxcf->mode = GOOD;
+  oxcf->cfg = &cfg->cfg;
 
   switch (cfg->g_pass) {
     case AOM_RC_ONE_PASS: oxcf->pass = 0; break;
@@ -1886,15 +1887,16 @@
         2000,  // rc_two_pass_vbrmax_section
 
         // keyframing settings (kf)
-        AOM_KF_AUTO,  // g_kfmode
-        0,            // kf_min_dist
-        9999,         // kf_max_dist
-        0,            // large_scale_tile
-        0,            // monochrome
-        0,            // tile_width_count
-        0,            // tile_height_count
-        { 0 },        // tile_widths
-        { 0 },        // tile_heights
+        AOM_KF_AUTO,               // g_kfmode
+        0,                         // kf_min_dist
+        9999,                      // kf_max_dist
+        0,                         // large_scale_tile
+        0,                         // monochrome
+        0,                         // tile_width_count
+        0,                         // tile_height_count
+        { 0 },                     // tile_widths
+        { 0 },                     // tile_heights
+        { CONFIG_EXT_PARTITION },  // config file
     } },
 };