stella: Update to 6.2.1

6.2 to 6.2.1: (June 20, 2020)

  * Fixed Pitfall II ROM not working correctly.

  * Fixed crashes when using some combinations of bankswitching schemes on
    incorrect ROMs, or when using invalid ROM file sizes, etc.

  * Fixed RIOT timer behaviour on reading/writing at the wraparound cycle.

  * Fixed incorrectly setting D6 bit on TIA reads in some cases.  Related
    to this, improve 'tiadriven' option to randomize only D5..D0 bits.

  * Fixed custom palette and TV effects adjustable slider rounding issue.

  * Fixed some bugs in 3E+ scheme when using non-standard ROM sizes.

  * Fixed crash in Audio & Video dialog when opened from debugger, and the
    debugger window sometimes being resized when using the Options dialog.

  * Make NTSC custom phase shift not affect Yellow anymore.

  * Fixed '1x' snapshot mode; TV effects are now disabled.  This mode
    now generates a clean, pixel-exact image.

  * Fixed mappings sometimes not being saved in the Retron77 port.

  * A ROM properties file may now be placed next to the ROM (with the same
    name as the ROM, except ending in .pro), and Stella will automatically
    apply the properties to the ROM. [NOTE: this was present in 6.2, but
    was mistakenly left out of the changelog]

  * Added button to Game Info dialog to save properties of the currently
    loaded ROM to a separate properties file (in the default save directory).
    This is useful in conjunction with the previous item.

  * Allow changing custom palette and TV effects adjustables in 1% steps
    again.

  * Updated documentation for changes in ROM properties key names.

  * The codebase now compiles under gcc6 again.  Future versions will
    require gcc7, though.

-Have fun!

(nia)