Fixed test for isprint.
Added a pretty printing method for indexes
Fixed conversion between Lisp arrays and Lush'
The pretty printer for indices always printed the same value
\^A returned char 0 instead of 1
Added more tests for reading special characters in strings.
Sequence \b means backspace, not bell
Test that str-cat always creates new strings
In str-mid, fixed handling of indices out of bounds.
Added tests for substring
Implement quirks from Lush2 into str-right/left
Check that arrays are created anew in str-right/left
Tests for str-insert
str-insert always returns a fresh new string
STR-DEL additional checks. STR-DEL always creates a new string.
STR-SPLIT always returns fresh new strings