Adding Host Primitives to a NeXtMidas option tree

Adding host primitives to a NeXtMidas option tree.
1. Make sure that XBC is on the path.
2. Create a buildopt.mm macro in the mcr area for the option tree.
  - Initially it can just look like this (be sure to change MYOPT to the name of the option tree):
```
! Calls the BUILDOPT;XBC to build the option tree.
startmacro u:option["MYOPT"]
  BUILDOPT;SYS/mfn="nxm.xbc.mcr.buildopt.mm" ^option
endmacro
```
3. Create a messages.cfg file in the cfg area of the option tree. (Optional)
4. Add the host primitive to the host area of the option tree. Then use UPDATE to add it to the dictionary (use H for the command support).
5. Build the option tree:
```
nM> MAKE ALL <OPT>
```
Verifying a host primitive will run in XBC
- The CHECKXBC;XBC command can be run manually to verify if a host primitive will run in XBC. See explain file for more details.