### Expand the use of colour in the IOCs output

This release includes various changes to iocsh.cpp and elsewhere to add and
expand the use of color:

- When loading a startup script, the IOC Shell now displays comment lines in
blue, and uses bold to make command lines stand out from other text.

- The `softIoc -v` output also uses the above color scheme for the commands it
prints.

- The default IOC Shell prompt is now displayed in green; this color can be
modified in the `configure/CONFIG_SITE_ENV` file for all targets, or set for
a specific target by adding a `configure/os/CONFIG_SITE_ENV.<arch>` file.
The value of the `IOCSH_PS1` environment parameter in those files can use the
`ANSI_ENV_*` and `ANSI_*()` color macros found in errlog.h to configure the
appearance of the prompt. The C string literal concatenation syntax can be
used to construct the prompt string:

```Makefile
    IOCSH_PS1 = ANSI_ESC_RED "e" ANSI_ESC_YELLOW "p" ANSI_ESC_GREEN "i" \
        ANSI_ESC_CYAN "c" ANSI_BLUE("s") "> "
```

- More error messages printed by IOC Shell commands now appear in red, or use
the red `ERROR` prefix that was introduced in previous releases.

- The word "Illegal" has been replaced with "Invalid" in several Shell error
messages.

- The iocsh `var` command now shows the data type of the registered variables
as well as their values.