Ra drop improvement

[norm-ideal]

Concerning the "Ra-Drop" error, as @hirokiky pointed out, the dictionary includes a wrong expression "見れる" as a correct word. It makes the detection of an error difficult.

We cannot rely on the dictionary that they do not have other such cases, so I tried to implement the logic by adding baseForm information as:

• if the words are "一段動詞・未然" + baseForm "れる", it is an error.
• if the baseForm of a verb ends with "れる" and not with "られる" ( a potential verb ):
  -- replace the "れる" with "る" to make it a normal verb ( such as "見れる" -> "見る" )
  -- if its inflection type is "一段" or "カ変", it is an error. ( the inflection type of "見る" is "一段", so it is an error. )

If there are no exceptional wrong verbs in the dictionary, @hirokiky 's method combined with baseForm information would be better because it is fast and simple.

[coveralls]

Coverage increased (+0.004%) to 91.415% when pulling 2aae17b on norm-ideal:ra-drop-improvement into 4341913 on redpen-cc:master.