TimeArray: accept duplicated but sorted time index

[iblislin]

julia> a = TimeArray([Date(2015, 10, 1), Date(2015, 10, 2), Date(2015, 10, 3)], [1,2,3]);

julia> b = TimeArray([Date(2015, 10, 2), Date(2015, 10, 3)], [4, 5]);

julia> [a; b]
5×1 TimeArray{Int64,1,Date,Array{Int64,1}} 2015-10-01 to 2015-10-03
│            │ A     │
├────────────┼───────┤
│ 2015-10-01 │ 1     │
│ 2015-10-02 │ 2     │
│ 2015-10-02 │ 4     │
│ 2015-10-03 │ 3     │
│ 2015-10-03 │ 5     │

[codecov-commenter]

Codecov Report

Merging #455 into master will decrease coverage by 0.05%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #455      +/-   ##
==========================================
- Coverage   89.52%   89.47%   -0.06%     
==========================================
  Files          12       12              
  Lines         611      608       -3     
==========================================
- Hits          547      544       -3     
  Misses         64       64              

Impacted Files	Coverage Δ
src/TimeSeries.jl	100.00% <ø> (ø)
src/utilities.jl	100.00% <ø> (ø)
src/combine.jl	98.76% <100.00%> (ø)
src/timearray.jl	97.20% <100.00%> (ø)

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