aqp 1.42

This is a retroactive release to tag the commit corresponding to last CRAN version (1.42) prior to the v2.0 release.

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What's Changed

• Test persistence of attributes and metadata in SoilProfileCollection by @brownag in #236
• Remove aqp::filter by @brownag in #238
• Implement required argument for SPC metadata by @brownag in #237
• Add as.character(<SoilProfileCollection>) by @brownag in #239
• Add accumulateDepths() by @brownag in #235
• fixes to estimateSoilDepth by @dylanbeaudette in #242
• repairMissingHzDepths: Use spc_horizonOffset() by @brownag in #246
• Empty SPC prototype should be able to preserve horizon names by @brownag in #245
• Texture by @smroecker in #244
• "spatial predicates" for horizon data by @brownag in #247
• slab(): pass formula argument to aggregate.formula(x, ...) by @brownag in #248
• spc2mpspline(): upgrades by @brownag in #250

Full Changelog: 1.31...1.42