[CLI Project] Switched command Parsing to YACC and LEX
As mentioned, I have pushed r67, that comprises of the improved command parsing system using Lex and YACC, for the Mailman shell. The PLY module is used for the purpose.
Every command has a parser script associated with it, under the
client/parsers/ directory. The parser is imported and used by each command
independently. The parser returns the necessary arguments as a hash
table, which can be easily used by the command execution
The change of command parsing method to PLY now handles both command validation and parsing/processing, which was previously done in independent command processing steps. The r67 also improves the environment variable management.