danlwarren/ENMTools: ENMTools 1.0.4

I forgot to create GitHub releases for versions 1.0.2 and 1.0.3, but I'm going to try to be good about it from now on. Here are the intervening changes:

• Raes and ter Steege-style tests were returning incorrect evaluate objects, although plots and p values were correct
• test.prop = "block" wasn't working correctly

• Suppressing maxent startup messages by default
• Added support for bias layers to modeling functions
• Added check.env function to homogenize raster stacks so NAs propagate across layers

• Brought up to date for new spatstat changes
• Removed ppmlasso until it is brought back on CRAN

• Added a new general-purpose function for making background layers from point data. It can do both circular buffers and buffered convex hulls, and can return points, a polygon, or a raster. Converted the existing background buffer functions to just call this one, and will eventually deprecate the single-application functions.
• Added ability to select which corner you want for "block" validation.
• Added a function called multi.variogram which takes a raster stack, builds a variogram for each layer, and then plots the gamma for each variable as a function of distance, scaled by the maximum gama for that variable. This allows users to get some idea of the level of spatial autocorrelation in each predictor variable.