Last FM refactor

[ThomasSmyth]

Extensive updates to last fm code that serve to both simplify and expand functionality.

• chart logic simplified by leveraging inbuilt api weekly chart requests.
• charts and top requests now have exactly the same filters, allow the same column logic to be used for both.
• addition of album filter.
• can now request total number of scrobbles for a user or all users.
• help message now includes info on new methods.

[jonathonmcmurray]

you use `$"@attr" all over the place - any chance you could just use .Q.id on the api results and then use `attr? Maybe with the level of nesting in the returned object that is infeasible

I think it's possibly just a dict, in which case something like:

q){.Q.id'[key x]!get x} (enlist`$"@attr")!enlist 123
attr| 123

Should work. Perhaps it would be useful to have a utility function like this, seeing as there are often things like this in API returned JSONs

q){$[99h=type x;.Q.id'[key x]!get x;.Q.id x]} (enlist`$"@attr")!enlist 123
attr| 123
q){$[99h=type x;.Q.id'[key x]!get x;.Q.id x]} enlist (enlist`$"@attr")!enlist 123
attr1
-----
123

[ThomasSmyth]

Added purge function as qid.

[jonathonmcmurray]

Nice qid function @vibronicshark55