Refactoring

[ickc]

Currently, pantable and pantable2csv are provided. But the naming is not ideal (what if more formats will be added, as in #8?).

One option is to let pantable accept args, but it is not easy: https://groups.google.com/d/msg/pandoc-discuss/LIAfgkZKUiE/HWr_1k13EgAJ

Another problem is, if I want it to be a "simple filter" in the pandocpm sense (pandoc-extras/pandocpm#7), then it has to be a single self-containing filter like pantable and pantable2csv currently are.

It also depends on #8, if other formats are supported such that an extra dependency is needed, then there's no point for it to be all in 1 file, since it is not self-contained anyway.

On one hand, I want to wait to see if filter arg will be supported in pandoc first, on the other hand, the later I make such change, the higher the backward-ompatibility problem will becomes.

[ickc]

Refactoring is done. Other stuffs mentioned is in #10.