LittleDict / OrderedDict pop! consistency

[mattBrzezinski]

@iamed2 pointed this out in #59, here. We do not have consistency between the pop! function for LittleDict and OrderedDict.

LittleDict

Will return nothing if the key is not found.

OrderedCollections.jl/src/little_dict.jl

Lines 239 to 251 in 5fb23d8

	function Base.pop!(dd::UnfrozenLittleDict, key)
	@assert length(dd.keys) == length(dd.vals)
	for ii in 1:length(dd.keys)
	cand = @inbounds dd.keys[ii]
	if isequal(cand, key)
	deleteat!(dd.keys, ii)
	val = @inbounds dd.vals[ii]
	deleteat!(dd.vals, ii)
	return val
	end
	end
	end

OrderedDict

Will throw a KeyError if the key is not found.

OrderedCollections.jl/src/ordered_dict.jl

Lines 380 to 383 in 5fb23d8

	function pop!(h::OrderedDict, key)
	index = ht_keyindex(h, key, false)
	index > 0 ? _pop!(h, index) : throw(KeyError(key))
	end

I propose that we make the following changes:

1. Have LittleDict throw a KeyError when the key is not found.
2. Introduce a new function which provides a default value to return if key DNE (LittleDict pop! default #59)

[iamed2]

In support:

julia> pop!(Dict(), "baz")
ERROR: KeyError: key "baz" not found
Stacktrace:
 [1] pop!(::Dict{Any,Any}, ::String) at ./dict.jl:570
 [2] top-level scope at REPL[3]:1