Improve handling of nul-terminated string in Globals.

[galenh]

• When StringType size is calculated, save it to the underlying ArrayType.
• Re-used existing DataTypes from Globals instead of re-creating them when collecting types.
• Fix an inverted "<=" error.
• Print linear arrays on a single line.

[uxmal]

Hello @galenh ; thanks for your PR. I have some comments that need to be addressed before accepting it. Also, as a new contributor, don't forget to add yourself to the AUTHORS file!