plus4emu 1.2.4 release

Changes in version 1.2.4:

* implemented the ACIA 6551 registers at $FD00-$FD0F, which are automatically enabled for configurations with 64K or more RAM; this is not complete yet, but the basic functionality works
* video recording can also be done in RLE8 format now, which allows smaller file sizes than uncompressed YV12, at the expense of some TV emulation effects not being captured
* added new command line option for selecting the GUI style and colors
* various minor improvements and bug fixes