Improve right-justification mode

With this commit you can right-align the last token with * or ** field number.
For example, the following lines
    a = 1
    bb = 22
    ccc = 333
are aligned as follows on `:EasyAlign**=`
    a   =   1
    bb  =  22
    ccc = 333
And even if we don't have the second =, we can do `:EasyAlign!2=` to get
    a =     1
    bb =   22
    ccc = 333