FILE command

The FILE Command:
- The FILE command is used to perform I/O on a file from a macro.
```
nM> FILE <func> <label> ...
```
- The FILE command can manipulate any of the file types for which there is a file handler, not just Midas Blue files.
  - NeXtMidas automatically selects the appropriate file handler to use; however, there are options that allow this to be overridden.
```
nM> file open fileTag airports.csv{headerrows=1}
nM> invoke ,, fileTag.getDataTable(42)
Invoke: ANSWER = {AIRPORT_NAME="Avalon",CODE="AVL",
                  LATITUDE="-038.04083",LONGITUDE="144.46806"}
nM> file close fileTag
```
    (Note that fileTag can be any results parameter name, this is just a simple example.)
- A typical usage is to OPEN the file, READ from it or WRITE to it, then close it. (OPEN/N can be used to create a new file.)
```
nM> file open/d/n fileTag my_really_long_file_name{sr=(LAT/SD,LON/SD)}
nM> res fileTag.data(0,"LAT") 77.7
nM> res fileTag.data(0,"LON") 99.9
nM> file close fileTag
```
- In between the OPEN and CLOSE, the file is in memory and can be altered quickly.
  - While in memory, a file can is referenced by the provided <LABEL>.
- The FILE command has many other functions not outlined here (COPY, DETACH, NAME, RENAME, PROTECT, SAVE, etc.). See the explain file for FILE for details.

X-Midas Users Take Note:
The `PROTECT` and `UNPROTECT` functions in `FILE` are used in place of the X-Midas `PROTECT` and `UNPROTECT` commands. The `DETACH` function in `FILE` is used in place of the X-Midas `DETACH` command (since NeXtMidas 2.9.1.) The `OPEN` and `CLOSE` functions work similar to the X-Midas `ENV FILE OPEN` command.