Bugfix Real Graphics modes

[craigthomas]

This PR fixes a number of bugs with real graphics modes. In particular, GxR and GxC modes were not drawing pixels correctly on the screen. This PR also implements composite artifact colors for screen mode G6R. This PR also attempts to start sorting out the PIA data direction registers as well as the PIA control registers.

[codecov]

Codecov Report

Merging #27 into master will increase coverage by 1.09%.
The diff coverage is 11.23%.

@@             Coverage Diff              @@
##             master      #27      +/-   ##
============================================
+ Coverage     67.66%   68.76%   +1.09%     
+ Complexity     1025     1024       -1     
============================================
  Files            43       43              
  Lines          4856     4790      -66     
  Branches        487      432      -55     
============================================
+ Hits           3286     3294       +8     
+ Misses         1479     1405      -74     
  Partials         91       91

Impacted Files	Coverage Δ	Complexity Δ
.../craigthomas/yacoco3e/datatypes/G3RScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../craigthomas/yacoco3e/datatypes/G1CScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...craigthomas/yacoco3e/datatypes/SG12ScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../craigthomas/yacoco3e/datatypes/G2RScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../craigthomas/yacoco3e/datatypes/G3CScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../craigthomas/yacoco3e/datatypes/G1RScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../craigthomas/yacoco3e/datatypes/G2CScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../craigthomas/yacoco3e/datatypes/G6RScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
.../craigthomas/yacoco3e/datatypes/G6CScreenMode.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...n/java/ca/craigthomas/yacoco3e/components/CPU.java	95.62% <100%> (+0.01%)	514 <6> (ø)	⬇️
... and 3 more

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