This is an attempt to rearrange configure --help output a bit
and consolidate pairs of --enable/disable into its own section.

After this, help text is easier to sort, manage and read.
More descriptive text can be added as well, since we now have
more space.

While at it, mention en/dis-able-vte.
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>