pyIEM 1.20.0 release

API Changes

• Change storage logic of SBW to not include CAN polygons in the case of
  a CAN/CON combination update (#888).
• Depend on docutils for reStructedText to HTML conversion.
• Don't generate jabber messages for LSR products with more than 4 LSRs (#901).
• util.get_autoplot_context can now raise IncompleteWebRequest.
• The VTEC/SBW database storage of raw NWS product text was discontinued.
  Instead, raw product_id values are stored, which can be used against IEM
  web services to get the raw text. (#857)

New Features

• Account for common AM/PM typos and off-by-one year timestamps in NWS Prods.
• Add backgroundcolor option to MapPlot.plot_values.
• Add comprehensive_climate_index and temperature_humidity_index.
• Add imgsrc_from_row helper for SPC outlook link generation.
• Add parse_commas option to webutil.ensure_list, so to allow comma
  delimited CGI params by default.
• For pydantic schema based iemapp, keys like wfo[] go to wfo.
• Introduce some pydantic based validators for web requests, experimental...
• Store product_signature in sbw table (requires iem-database schema update).
• Support SPC corrections for MCDs so to prevent database dups.

Bug Fixes

• Allow for pydantic field validation to work when there's legacy year vs
  year1 present.
• Correct generated LSR summary link to have timestamps in UTC.
• Correct handling of is_emergency when done within VTEC correction (#899).
• Correct SKC parsing within TAFs, level is now None in this case (#453).
• Don't allow CF6 data from "today" or the "future" to be parsed, if missing.
• Fix numeric instability with pyiem.plot.centered_bins (#871).
• Forward propagate sbw database storage of VTEC issuace (#862).
• Handle edge case with NWS text product having a polygon at the end without
  a trailing newline (ancient text).
• Improve NWS Text Product signature logic so to more generally match what
  looks like a signature (#865).
• Improved NWS MND header logic for timestamp retrieval.
• Make better life choices attempting to glean a NWS Text Product signature.
• Prevent situation in sbw database having polygon_begin > polygon_end (#862).
• Refactor VTEC/SBW storage logic to use vtec_year column and operate on the
  parent table (#863).
• Update link to new NWPS website.