feat(library/aliases): remove duplicates from aliasing tables

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean/class): allow many instances to provided with a single 'instance' command

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/standard): add namespace 'pair'

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean/builtin_cmds): allow many namespaces in the same 'using' command

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/aliases): aliasing behavior

The new test '../../tests/lean/run/alias3.lean' demonstrates the issue being fixed.

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): rename command 'reset_proof_qed' to 'set_proof_qed'

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): remove [class] annotation and 'class' command, they are redundant, we only need [instance] and 'instance'

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>