Fix bugs in shift and hcat for MVTSeries

[bbejanov]

Bug in shift is that it updates only the first date of the MVTSeries, but not the firstdate of the individual columns TSeries views. As a result, rangeof(lag(A)) is shifted, but rangeof(lag(A).a) is not.

The bug is hcat is that the range of the result is the range of the first argument and does not take into account the rest of the arguments. In the updated version the range of the result is calculated as the rangeof_span of all arguments that are to hcat'd.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.73%. Comparing base (e072557) to head (ae61563).

Additional details and impacted files

@@                  Coverage Diff                  @@
##           65-rename-columns      #69      +/-   ##
=====================================================
+ Coverage              93.70%   93.73%   +0.02%     
=====================================================
  Files                     24       24              
  Lines                   4800     4807       +7     
=====================================================
+ Hits                    4498     4506       +8     
+ Misses                   302      301       -1     

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