update docs: cph() continuous phase graph function
added operator "cph()" to transform discontinuous phase ph(xxx) in AC analyses to aontinuous phase, like ngspice cph() function. Usage: instead of ph(out) use "ph(out) cph()"
change_elem_order(): use input_line instead of text_line dialog
add "Properties" menu for "Change selected object insertion order" (Shift-S)
further streamlined hash lookup functions
simplified hash table lookup functions (indirect pointer)
small cosmetic changes in hash tables (initialization of next pointer)
added mux21.sch and mux21.sym in logic/, testcase in testbench.sch