add search method

    search <scope> <text> <count> [<username>]
    
    search text in known data
    <scope> is data area: messages, directmsgs, profiles, users, hashtags
    <text> is a phrase to search
    up to <count> entries are returned
    <username> in messages scope is optional and allows to search in username's messages only
    <username> in directmsgs scope is required and sets whose conversation to search