Change hash function to use 2 argument version

[adranka]

Some changes to the way hash is implemented in the package:

• Changes the hash function to use the 2 argument version as recommended in the Julia docs
• Applies the hash function recursively
• Makes BusinessDays.jl free of invalidations (at least with Base)

Before:

julia> using SnoopCompileCore

julia> invs = @snoop_invalidations using BusinessDays
Precompiling BusinessDays finished.
  1 dependency successfully precompiled in 2 seconds
SnoopCompileCore.InvalidationLists(Any[], Any[MethodInstance for Base.hashindex(::Any, ::Int64), 1, MethodInstance for Base.rehash!(::Dict, ::Int64), 2, MethodInstance for Base.var"#sizehint!#303"(::Bool, ::typeof(sizehint!), ::Dict, ::Int64), 3, MethodInstance for sizehint!(::Dict, ::Int64), 4, MethodInstance for (::Type{Dict{_A, _B}} where {_A, _B})(::Tuple{Pair{String, String}, Vararg{Pair}}), 5  …  MethodInstance for Base.var"#showerror#822"(::Bool, ::typeof(showerror), ::IOContext{Base.TTY}, ::BoundsError, ::Vector{Base.StackTraces.StackFrame}), 3, MethodInstance for Core.kwcall(::@NamedTuple{backtrace::Bool}, ::typeof(showerror), ::IOContext{Base.TTY}, ::BoundsError, ::Vector{Base.StackTraces.StackFrame}), 4, MethodInstance for Base.var"#showerror#822"(::Bool, ::typeof(showerror), ::IOContext{Base.TTY}, ::MethodError, ::Vector{Base.StackTraces.StackFrame}), 3, MethodInstance for hash(::Any), "jl_method_table_insert", hash(a::BusinessDays.Australia) @ BusinessDays ~/code/original_code/BusinessDays.jl/src/calendars/australia.jl:35, "jl_method_table_insert"])

julia> using SnoopCompile, AbstractTrees

julia> trees = invalidation_trees(invs)
1-element Vector{SnoopCompile.MethodInvalidations}:
 inserting hash(a::BusinessDays.Australia) @ BusinessDays ~/code/original_code/BusinessDays.jl/src/calendars/australia.jl:35 invalidated:
   backedges: 1: superseding hash(x) @ Base hashing.jl:28 with MethodInstance for hash(::Any) (1400 children)

After:

julia> using SnoopCompileCore

julia> invs = @snoop_invalidations using BusinessDays
Precompiling BusinessDays finished.
  1 dependency successfully precompiled in 2 seconds. 3 already precompiled.
SnoopCompileCore.InvalidationLists(Any[], Any[])

julia> using SnoopCompile, AbstractTrees

julia> trees = invalidation_trees(invs)
SnoopCompile.MethodInvalidations[]

@felipenoris Let me know if this looks good!