don't use migemo when a current line doesn't contain any multibyte character

    This feature is enabled when g:clever_f_across_no_line is 1
improve a default value of g:clever_f_use_migemo

migemo search seems to be heavy in some cases
add some lines for my favorite layout
cache a previous pattern while repetition
fix initial value of s:first_move[mode]
todo to make migemo support faster
tiny refactoring