Place NAs just in C code (2d case)
Rename and dotify factor.mask & field.weights (for 2d case)
Rename area_indices struct
Factor masks' struct and init code into separate .h/.c files
Rename col_ind <--> row_ind
Fix .traj.dim.2d.ssa
Add `is.shaped` helper
Add circular shaped 1d-ssa
Allow PSSA be shaped
MSSA is not shaped
Disable forecasting and parest for shaped case
Fix wnorm and wcor for 1d-shaped case
Merge pull request #162 from eodus/sh1dv3

Add shaped 1D SSA