Use structs for element factory

[twsouthwick]

This helps a bit with performance:

Before

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
Create	41.71 us	0.776 us	0.762 us	6.1035	0.2441	51.52 KB
CreateNoSave	40.32 us	0.729 us	0.780 us	6.1035	0.2441	51.52 KB
ReadFile	847.70 us	16.828 us	29.474 us	29.2969	3.9063	255.22 KB

After

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
Create	40.80 us	0.665 us	0.589 us	6.1035	0.2441	51.52 KB
CreateNoSave	40.50 us	0.561 us	0.438 us	6.1035	0.2441	51.52 KB
ReadFile	830.07 us	14.996 us	22.446 us	29.2969	3.9063	255.22 KB