placement support

[raphamorim]

adds few parameters:

• aw — authored advance width, in upm units. The intended
  horizontal extent of the glyph, NOT the outline's bounding box.
  Optional; default upm.
• lh — authored line height, in upm units. The intended vertical
  extent (descender-to-ascender), NOT the outline's bounding box.
  Optional; default upm.
• width — the codepoint's Unicode width, in the wcwidth /
  UAX 11 sense. One of 1 (narrow) or 2 (wide). Optional;
  default 1. Authoritative for all terminal layout decisions
  (cursor advance, wrapping, selection geometry), overriding the
  codepoint's UAX 11 East Asian Width (all PUA ranges are
  Ambiguous by default).
• size — scale policy. One of height, advance, contain,
  cover, stretch. Optional; default height.
• align — placement of the scaled outline within the render span,
  as a comma-separated pair <h>,<v>. <h> is one of start,
  center, end; <v> is one of start, center, end,
  baseline. Optional; default center,center.
• pad — insets from the render span edges, as comma-separated
  fractions <top>,<right>,<bottom>,<left> (each 0.0–1.0;
  top/bottom are fractions of cell height, left/right of render
  span width). Optional; default 0,0,0,0.