X3: Missing examples

[Bockeman]

There are a number of examples (and possibly corresponding tutorials) for the following (which were present in older versions):

• calc/calc4c
• calc/calc7
• calc/calc8
• calc/calc9
• rexpr/rexpr_full

These may or may not be appropriate/useful for X3 (but I have ported these from before).
If not, then perhaps the user should be given an explanation of why not.

It would be really useful if the developers could supply some further examples of the usage of X3 in the more sophisticated or real world cases. There are many different ways of coding the same thing in X3.
It would be helpful if the user could be guided into best practice (for efficiency of coding, compile performance, runtime performance and so on).