Implements eval command and minor CLI cleanups.
Implemented eval command can be used to evaluate expressions.
The patch also documents echo command and allows to use log classesinstead of integer as a mask for echo.
Adds filtering to 'show symbols' command.
Thanks Alexander V. Chernikov for the original patch.
Implements command that shows memory usage.
Split off general commands to cmds.c.
Added `show symbols' command which dumps whole symbol table togetherwith symbol types etc.