Qualified imports of pkg/tt outnumber unqualified (27 to 24). Improve
consistency, and clarity, by changing the dot (unqualified) imports of
that package symbols to qualified.
Also remove support for the "name" field tag from eval.scanOptions - it's not
used anywhere and the use case it was intended for is handled by CamelToDashed.
This change makes feeding output to commands which handle NUL terminated
"lines" (e.g., `fzf -read0` or `xargs -0`) extremely fast compared to
using an explicit Elvish loop that does `print $val"\x00"`. Similarly for
handling input from commands that produce NUL terminated "lines" (e.g.,
`find . -print0`) compared to an Elvish loop using `read-upto "\x00"`.
Resolves#1070
Related #1053
Also remove unused functions.
There were two (correct) implementations of deciding whether a string has
another string as a subsequence; keep the more performant one.
