- Renamed 'sp_cond_type' to 'sp_condition_value'
    (it represents actually the condition *value* (in the Manual's terms));

  - Renamed 'sp_cond' to 'sp_condition'
    (it represents data for the whole DECLARE HANDLER statement);

  - Moved 'enum label_scope_type' into sp_context class;
    Renamed it to 'enum_scope' (it is actually a context scope);
    Renamed LABEL_DEFAULT_SCOPE to REGULAR_SCOPE;
    Renamed LABEL_HANDLER_SCOPE to HANDLER_SCOPE.

  - Moved 'enum sp_param_mode_t' into sp_variable class;
    Renamed it to 'enum_mode';
    Renamed 'sp_param_in' to 'MODE_IN';
    Renamed 'sp_param_out' to 'MODE_OUT';
    Renamed 'sp_param_inout' to 'MODE_INOUT'.

  - Introduced 'enum sp_label::enum_type { IMPLICIT, BEGIN, ITERATION }'.
    Replaced the following macros by this enum:
      - SP_LAB_IMPL
      - SP_LAB_BEGIN
      - SP_LAB_ITER