[color] fix transparency of colorized fonts

Thanks to Robert Schlicht and Will Robertson for the fix.
Fixes https://github.com/lualatex/luaotfload/issues/222

[0] http://tex.stackexchange.com/q/185878
[conf] allow spaces in formats specification

List items are now stripped of leading and trailing spaces before
building the formats list.
[conf] strip unused configuration variable

What the hell was that for?
[doc] describe configuration options
[main] deprioritize fontloader intro message

This message originates in ``luatex-fonts.lua`` [0]. The advice given on
using the Context libraries directly is counterproductive unless one is
already hacking on the Luaotfload code, in which case it should be
obvious anyways. Cluttering the log file with those lines is
unjustified.

[0] http://git.contextgarden.net/context/context/blob/master/tex/generic/context/luatex/luatex-fonts.lua#L139
[main] adapt local to current terminology
[tool] fix log level status message
 [tool] reorder task list to prevent the log level from being overridden due to configuration
[doc] extend documentation of config options in manpage
[tool] fix setting of verbosity
[conf] warn about unknown variables
[parsers] convert dashes to underscores in ini parser
[doc] fix variable identifiers
[doc] add short example file to configuration man page
[conf] add example configuration file
[conf] add example configuration file