Add print42 library page

Author: boriel

docs/library/print42.bas.md

@@ -0,0 +1,29 @@
+#Print42.bas
+
+The 42 column printing routine allows text to be 6 pixels wide instead of 8.
+It is NOT proportional printing, but this is still useful for lining things up in columns.
+
+This routine has been adopted as an included library - so you may include it with
+
+```
+#include <print42.bas>
+```
+
+##Usage
+
+```
+printat42(y,x)
+```
+
+Moves the print42 system's print cursor to row Y, column X. Note that `0 <= x <= 41` - that is the range of values
+for X can be up to 41. The range of values for Y is the normal 0-23.
+
+```
+printat42(STRING)
+```
+
+Prints the string to the screen at the current Print42 co-ordinates. It does so in the current permanent colours.
+
+NOTE: The ZX Spectrum's attribute system is encoded into the hardware as a 32 character grid. Print42 does its best,
+but changing the `paper`/`bright`/`flash` colour from the background is likely to look imperfect as the attribute blocks
+cannot line up well with the pixel blocks.