Getting the next word respects quoting and escaping.

Getting the next word respects quoting and escaping.

Use double quotes (").  They can be interspersed with
other whitespace characters, just like shell quoting.

A backslash (\) always escapes the next character.

The end of the stream always terminates the word.

Add AutoText struct to unit test utilities, to easily
make spv_text_t values and reference them as spv_text values.