Rename sexpr eqp to is_eqp

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
Enable automatic coercion from 'char const *' to hierachical name

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

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

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