Fix nth_value function
Use equals instead of == for Doubles in LiteralInterpreter
Disable DWRF String and Date statistics which are broken

The merge logic DWRF String and Date statistics are broken so the statistics
for stripes and files in DWRF can not be used for String and Date columns.
Ignore ORC and DWRF DoubleStatistics containing NaN

ORC and DWRF writer does not handle NaNs properly so any statistic involving a NaN should be ignored.
Fix lead, lag and nth_value
Fix whitespace
[maven-release-plugin] prepare release 0.81
[maven-release-plugin] prepare for next development iteration
Add current_timezone() function
Improve heuristic for creating symbols from name hints
Rename getOutputMap to getAssignments in project node
Compute output symbols eagerly

The list was being build on-demand every time getOutputSymbols was called, making
analysis/planning of queries with thousands of columns expensive
Optimize planning for queries with many columns

The code had a number of O(N^2) algorithms, which is ok for queries referencing
a few hundred columns but quickly breaks down for thousands of columns
Precompute the field indexes to avoid O(N) lookup

This helps when analyzing queries with thousands of fields