feat(library/hott): copy basic files to hott library

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(kernel/expr): add has_expr_metavar_strict

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(kernel/inductive): use has_expr_metavar_strict instead of has_expr_metavar

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(kernel/type_checker): error message position information

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(tests/lean/hott): add some of Vladimir's definitions as tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean): fix 'let' annotation placement and pretty printer

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean/pp): pretty print 'have' expressions

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean/pp): pretty print 'show' expressions

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