Repurpose L/R in RGUI to scroll to next letter.

A common feature in controller-based file selection pickers
is to be able to scroll to next letter in the alphabet.
Add RGUI scroll acceleration.
Slight tweaks.
Implement an idea for a start screen.
Use skeleton config as basis for new configs.
Resolve libretro core names in RGUI.
Use info files to resolve libretro names.
fix missing include
Merge pull request #323 from libretro/nextletterscroll

Repurpose L/R in RGUI to scroll to next letter.
Merge pull request #325 from libretro/libretrodesc

Resolve libretro core names in RGUI.
Add more info files
Move info files over to libretro-super
Update start screen, and add Help ... entry.
Only show start screen if rgui_show_start_screen is set.

Default to true, and set to false on first time.
Add description for rgui_show_start_screen in config.
Style nits to core_info. Compile it in.
Use consistent namespace for core_list.
Merge pull request #324 from libretro/initcommands

Implement an idea for a start screen.
Begin implementing core autoselect.
Some display tweaks.