Addition of achannels

[crazycatdevs]

Allows to list channels with a particular flag enabled

Found by: CrazyCat
Patch by: CrazyCat

One-line summary: Allows to list channels with a particular flag enabled

Additional description (if needed):
Add the tcl command achannels [flag]

• if flag is ommited, returns [channels]
• if flag is not a channel flag (or doesn't exists), returns an error
• else, returns channels with flag enabled

Test cases demonstrating functionality (if applicable):

• channel #test has +test flag (user defined), -inactive and +greet
• channel #eggdrop has -test, -inactive and +greet

.tcl achannels dummy
Tcl error: dummy is unknow or not flag attribute
.tcl achannels test
Tcl: {#test}
.tcl achannels inactive
Tcl: 
.tcl achannels greet
Tcl: {#test} #eggdrop