[dev][st] patch for selcopy

Hi there,

Here is a small patch for adding the functionality: double clicks to select
a word, and triple clicks to select a line.
A *word* is defined as some string which is placed between space characters
or boundary.
A *line* is defined as the content which starts from 0 to term.col.

I've tried it and it looks to work fine.
Hope it helps...：)

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h5f