create new package for stdpp-bitvector library

This is a step towards #204 (closed).

I was not quite sure which Coq logical path to use for this. For now I used stdpp.bv since always typing stdpp.bitvector seems a bit annoying, but the inconsistency may also be confusing. Opinions?

stdpp/tactics.v

@@ -774,6 +774,9 @@ Tactic Notation "select" open_constr(pat) tactic3(tac) :=
       so then shelved goals are produced for every such evar. *)
   | H : pat |- _ => let T := (type of H) in unify T pat; tac H
   end.
+
+(** We provide [select] variants of some widely used tactics. *)
+
 (** [select_revert] reverts the first hypothesis matching [pat]. *)
 Tactic Notation "revert" "select" open_constr(pat) := select pat (fun H => revert H).
 
@@ -785,6 +788,15 @@ Tactic Notation "destruct" "select" open_constr(pat) :=
 Tactic Notation "destruct" "select" open_constr(pat) "as" simple_intropattern(ipat) :=
   select pat (fun H => destruct H as ipat).
 
+Tactic Notation "inversion" "select" open_constr(pat) :=
+  select pat (fun H => inversion H).
+Tactic Notation "inversion" "select" open_constr(pat) "as" simple_intropattern(ipat) :=
+  select pat (fun H => inversion H as ipat).
+Tactic Notation "inv" "select" open_constr(pat) :=
+  select pat (fun H => inv H).
+Tactic Notation "inv" "select" open_constr(pat) "as" simple_intropattern(ipat) :=
+  select pat (fun H => inv H as ipat).
+
 (** The tactic [is_closed_term t] succeeds if [t] is a closed term and fails otherwise.
 By closed we mean that [t] does not depend on any variable bound in the context.
 axioms are considered closed terms by this tactic (but Section