VisiData v0.98, now with graphs and maps (experimental)

When I announced that v0.97 was "feature complete", I must have been talking about vdtui.
vdtui has been pretty stable, even as VisiData has added a low-resolution pixel canvas
(using Braille unicode characters) to draw graphs and maps. In fact, apart from a few bug
fixes and small API changes, the only addition to vdtui in v0.98 is basic mouse support.

Here's a list of what's new in VisiData v0.98:

• visidata.org revamp

• [canvas] graphs and maps!

  • . or g. to push a graph or a map from the current sheet (dot=plot)
  • supports .shp and vector .mbtiles
  • mouse left-click/drag to set cursor
  • mouse right-click/drag to scroll canvas
  • scrollwheel to zoom in/out on a canvas
  • s/u to select/unselect rows at canvas cursor
  • ENTER to push source sheet with only rows at canvas cursor
  • 1-9 to toggle display of 'layers' (colors)
  • _ to zoom out to full width
  • disp_pixel_random option chooses pixel attrs at random (weighted), instead of most common
  • +/- to zoom in/out via keyboard

• Updates to commands

  • Remove ` (backtick) command
  • Remove most zscroll commands (zs/ze)
    • zz moves cursor to center, uncertain about the future of zt due to conflict with t for toggle
  • ga adds N new rows
  • gz= sets value for selected/all rows to a Python sequence in this column
  • z_ sets column width to given value
  • z- cuts column width in half
  • P is now "paste before" (like vim); R now pushes a random sample
  • ^Z now sends SIGSTOP; ^O "opens" the external $EDITOR (from builtin line editor)
  • [ColumnsSheet] Added ~!@#$ commands back, to set type of source columns
  • w is becoming a more universal "visibility toggle"
    • [TextSheet] w toggles wordwrap
    • [canvas] w toggles display of the labels
    • [pyobj] w toggles hidden properties and methods

• Updates to command line args and options

  • set initial row/col with +<row#>:<col#> (numeric only)
  • --delimiter/-d option (separate from --csv-delimiter) sets delimiter for tsv filetype
  • --replay-wait/-w renamed from --delay/-d
  • disp_date_fmt option for date display format string (default is date-only)
  • zero_is_null/empty_is_null/none_is_null/false_is_null set which values are considered null (previously was aggr_null_filter)
  • --skiplines option renamed to --skip, and --headerlines to --header

• Design improvements

  • Add specific rowtype for each sheet (see right status)
  • dates are a kind of numeric type (useful for graphing as the x-axis)
  • use_default_colors (at behest of @wavexx)
  • more robust Progress indicator
  • populate DescribeSheet in async thread
  • remove default names for unnamed columns
  • history up/down in edit widget now feels right

• API changes

  • change main Column API to getter(col, row) and setter(col, row, val)
  • move Path and subclasses out of vdtui
  • TextSheet source is any iterable of strings
  • Sheet.filetype provides default save filename extension

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