NotEqual operation implemented.

Also, some clean ups done in expressions.
`wild_card_compare' function added to database functions.

Related to issue #15
Wild Card added to libtocc and CLI.

1) WildCardExpr added to libtocc.
2) "=" operator of CLI's query, now invoke WildCardExpr by default.

Issue #15
NotEqual expression added to API, and "!=" and "~" operator added to CLI.

Issue #15
Directory of NotEqual tests changed according to new standard: /tmp/tocctests/
Merge branch 'issue15'

NotEqual implemented.