Merge branch 'jk/ansi-color'

The output coloring scheme learned two new attributes, italic and
strike, in addition to existing bold, reverse, etc.

* jk/ansi-color:
  color: support strike-through attribute
  color: support "italic" attribute
  color: allow "no-" for negating attributes
  color: refactor parse_attr
  add skip_prefix_mem helper
  doc: refactor description of color format
  color: fix max-size comment

Documentation/config.txt

@@ -150,27 +150,34 @@ integer::
        1024", "by 1024x1024", etc.
 
 color::
-       The value for a variables that takes a color is a list of
-       colors (at most two) and attributes (at most one), separated
-       by spaces.  The colors accepted are `normal`, `black`,
-       `red`, `green`, `yellow`, `blue`, `magenta`, `cyan` and
-       `white`; the attributes are `bold`, `dim`, `ul`, `blink` and
-       `reverse`.  The first color given is the foreground; the
-       second is the background.  The position of the attribute, if
-       any, doesn't matter. Attributes may be turned off specifically
-       by prefixing them with `no` (e.g., `noreverse`, `noul`, etc).
+       The value for a variable that takes a color is a list of
+       colors (at most two, one for foreground and one for background)
+       and attributes (as many as you want), separated by spaces.
 +
-Colors (foreground and background) may also be given as numbers between
-0 and 255; these use ANSI 256-color mode (but note that not all
-terminals may support this).  If your terminal supports it, you may also
-specify 24-bit RGB values as hex, like `#ff0ab3`.
+The basic colors accepted are `normal`, `black`, `red`, `green`, `yellow`,
+`blue`, `magenta`, `cyan` and `white`.  The first color given is the
+foreground; the second is the background.
 +
-The attributes are meant to be reset at the beginning of each item
-in the colored output, so setting color.decorate.branch to `black`
-will paint that branch name in a plain `black`, even if the previous
-thing on the same output line (e.g. opening parenthesis before the
-list of branch names in `log --decorate` output) is set to be
-painted with `bold` or some other attribute.
+Colors may also be given as numbers between 0 and 255; these use ANSI
+256-color mode (but note that not all terminals may support this).  If
+your terminal supports it, you may also specify 24-bit RGB values as
+hex, like `#ff0ab3`.
++
+The accepted attributes are `bold`, `dim`, `ul`, `blink`, `reverse`,
+`italic`, and `strike` (for crossed-out or "strikethrough" letters).
+The position of any attributes with respect to the colors
+(before, after, or in between), doesn't matter. Specific attributes may
+be turned off by prefixing them with `no` or `no-` (e.g., `noreverse`,
+`no-ul`, etc).
++
+For git's pre-defined color slots, the attributes are meant to be reset
+at the beginning of each item in the colored output. So setting
+`color.decorate.branch` to `black` will paint that branch name in a
+plain `black`, even if the previous thing on the same output line (e.g.
+opening parenthesis before the list of branch names in `log --decorate`
+output) is set to be painted with `bold` or some other attribute.
+However, custom log formats may do more complicated and layered
+coloring, and the negated forms may be useful there.
 
 pathname::
 	A variable that takes a pathname value can be given a