switch to using Dates.jl instead of Calendar.jl

[WestleyArgentum]

I haven't done all the testing in the world, but so far this works pretty well.

It also happens to fix the ambiguity warnings we get when using HttpCommon and DataArrays at the same time, see JuliaStats/DataArrays.jl#115, #6, etc

Would love feedback!

[jiahao]

cc @quinnj

[quinnj]

Ok @WestleyArgentum, we can actually do better! I actually had some work on parsing/formatting for days of the week, and so I cleaned up that code and pushed the changes. You can now do

julia> using Dates

julia> Dates.format(DateTime(2014),Dates.RFC1123Format)
"Wed, 01 Jan 2014 00:00:00"

So I believe this removes the need for ICU as well. Care to update the PR?

[WestleyArgentum]

That's awesome! Did you write that without introducing a dependence on ICU?

I'll look at the code and update this!

[WestleyArgentum]

Oh, missed your mention of ICU haha, nice!

[quinnj]

Yeah, nowutc() is now defined in Dates.jl as well, so no need to define it here.

[WestleyArgentum]

Oh! Didn't see that change - will include it