GitLab

This fixes issue #65.

Rename:

- prefix_of -> prefix and suffix_of -> suffix because that saves keystrokes
  in lemma names. However, keep the infix notations with l1 `prefix_of` l2 and
  l1 `suffix_of` l2 because those are easier to read.
- change the notation l1 `sublist` l2 into l1 `sublist_of` l2 to be consistent.
- rename contains -> submseteq and use the notation ⊆+

This patch was created using

  find -name *.v | xargs -L 1 awk -i inplace '{from = 0} /^From/{ from = 1; ever_from = 1} { if (from == 0 && seen == 0 && ever_from == 1) { print "Set Default Proof Using \"Type*\"."; seen = 1 } }1 '

and some minor manual editing

These just make things more complicated, it would be more useful to
declare (efficient) decision procedures for each instance, so that
we can properly predict which instance we will get.

Thanks to Amin Timany for the suggestion.

It is doing much more than just dealing with ∈, it solves all kinds
of goals involving set operations (including ≡ and ⊆).

simplify_equality        => simplify_eq
simplify_equality'       => simplify_eq/=
simplify_map_equality    => simplify_map_eq
simplify_map_equality'   => simplify_map_eq/=
simplify_option_equality => simplify_option_eq
simplify_list_equality   => simplify_list_eq
f_equal'                 => f_equal/=

The /= suffixes (meaning: do simpl) are inspired by ssreflect.

Also, make our redefinition of done more robust under different
orders of Importing modules.

Also do some minor clean up.

This one (previously solve_elem_of) was hardly used. The tactic that uses
naive_solver (previously esolve_elem_of, now solve_elem_of) has been
extended with flags to say which hypotheses should be cleared/kept.