implement g:eskk#log_{cmdline,file}_level

- update docs
- deprecate g:eskk#debug
  - use g:eskk#log_{cmdline,file}_level instead
vitalize for Mapping.options_chars2dict()
fix #173: conversion at command-line raises an error
#174 change exception to warning in get_begin_col().
Merge branch 'master' into multi_dictionary