NSH:  Add a break command; if-then-else and looping behavior can not be configured out of the build for small systems that need minimal scripting capability

NSH:  Loosen up if-then-else-fi syntx so that a command can be on the same line as the 'then' and 'else' tokens.  This allows, as an example, 'if true; then echo true; else echo false; fi' which is much more bash-like

If write buffering is enabled, then it is necessary to release the write buffer resources (callback structure) when the socket is closed

NSH can not handle command arguments that are concatenations of constant strings, command output, application program output, and environment varaible values.

NSH: Separate command line parsing from command execution.  Add support for multiple, semicolone separated commands on each line

NSH: Code expects CONFIG_NSH_DRIPADDR and CONFIG_NSH_NETMASK even if DHCPC is necessary.  For now, just removed the dependency on DHCPC in the Kconfig file, but more thought is needed.