Add get_FAC1_via_INDEX

Also change to only use bit 7 as sign in FAC1 and FAC2 (as the original BASIC does) to simplify
implementations.

strings/04B122856588B122856488B122856388B12285660980856288B1228561847060

@@ -0,0 +1,3 @@
+$04 + LDA ($22),Y + STA $65 + DEY + LDA ($22),Y + STA $64 + DEY + LDA ($22),Y + STA $63 + DEY + LDA ($22),Y + STA $66 + ORA #$80 + STA $62 + DEY + LDA ($22),Y + STA $61 + STY $70 + RTS
+
+Load FAC1 (well known zero page locations) from memory using well known vector in zero page (INDEX)

strings/20A2BB4C

@@ -0,0 +1,3 @@
+JSR $BBA2 + JMP fragment
+
+Call to well known floating point function + fragment

strings/60202BBC85

@@ -0,0 +1,5 @@
+60 20 2B BC 85
+
+RTS + JSR $BC2B + STA fragment
+
+Fragments + call to well known floating point function

strings/6E0980856A88B1228569A56160

@@ -0,0 +1,3 @@
+$6E + ORA #$80 + STA $6A + DEY + LDA ($22),Y + STA $69 + LDA $61 + RTS
+
+Fragment of copying using a well known index vector from a mem float into FAC2

strings/A004B122856D88B122856C88B122856B88B122856E

@@ -0,0 +1,3 @@
+LDY #$04 + LDA ($22),Y + STA $6D +  DEY + LDA ($22),Y + STA $6C + DEY + LDA ($22),Y + STA $6B + DEY + LDA ($22),Y + STA $6E
+
+Load parts of the mantissa of FAC2 and its sign (well known zero page locations) from memory using well known vector in zero page (INDEX)

strings/A9A8A0AE20A2BB4C

@@ -0,0 +1,3 @@
+LDA #$A8 + LDY #$AE + JSR $BBA2 + JMP fragment
+
+Loading well known address of math constant pi into AY and call well known floating point function (mov_MEM_FAC1)

strings/B124456630

@@ -0,0 +1,3 @@
+LDA ($24),Y + EOR $66 + BMI fragment
+
+Compare signs of FAC1 and float pointed to by index vector