classifier-gtk: add an option to start in full-screen mode
classify: remove duplicate line
text-classify.jl was getting nowhere. Begone!
test_backprop: move more opt_* globals out of load_or_create_net

Specifically, clean up the load branch.
test_backprop: make fp exception level a runtime option
charmodel: use a struct for alphabet; tug at test_backprop knots

In several places, the alphabet and collapse_chars arrays were being
passed around with their lengths, and the functions signatures all
contained this:

    int *alphabet, int a_len, int *collapse_chars, int c_len,

Now there is a struct that contains all that, simplifying stuff here and
there.

This began as an attempt to further untangle test_backprop, and at least
the rnn_char_check_metadata() function has come out of load_or_create_net()
into the charmodel library.

text-classify has not been keep up to date, since it doesn't work
properly anyway. This is symbolic punishment for it.
test/test_random: more thorough examination of gaussian curves.

This shows that the singlecheap approximation is *not* identical to the
doublecheap versions.
test_backprop: use net metadata for alphabet in confab only case.
charmodel urlencode: beware of signedness for high bytes
Add a text-confabulate executable

This does what test_backprop --confab-only did, but with less irrelevant
options.

It was necessary to let RnnCharAlphabet know whether it uses utf-8, which
should be spread elsewhere.
test_backprop: remove --confab-only

See instead text-confabulate, previous commit.
text-classify at least compiles again

But I still hate it.
charmodel: let alphabet struct carry round related flags