Add all possible units from IEEE488.2 to address some points of #26

Jan Breuer

2016-02-22 e7d3092dd149ce455eaa934cc63104b6273302f5

 libscpi/inc/scpi/expression.h

@@ -41,7 +41,7 @@
#ifdef __cplusplus
extern "C" {
#endif
    

    enum _scpi_expr_result_t {
        SCPI_EXPR_OK = 0,
        SCPI_EXPR_ERROR,