Fix handling of attached retroflex in pinyinize

[noe]

The CC-CEDICT syntax wiki describes the retroflex finals as:

There are 3 kinds of R-ised words that use the 兒/儿 character:

兒/儿 is not-optional because it's its own syllable (usually meaning “son,” so daughter is actually “girl son”) - 女兒/女儿 nǚ'ér
兒/儿 is not-optional because it changes the definition of the word and is tacked on to the preceding syllable - 头兒/头儿 tóur (leader) as opposed to 头 tóu (head)
兒/儿 is an optional northern pronunciation (er2hua4) and is tacked on to the preceding syllable - 花兒/花儿 huār (flower) as opposed to 花 huā (flower)
These 3 cases should be formatted as follows:

女兒 女儿 [nu:3 er2] /daughter/
頭兒 头儿 [tou2 r5] /leader/
花兒 花儿 [hua1 r5] /erhua variant of 花/flower/

However, in pycedict, cases 2 and 3 are not properly handled by pinyinize. The problem is two fold:

1. pinyinize assumes the syllable has vowels, so with r5 it fails at vowels = list(vowels).
2. The final retroflex is not attached to the previous sillable.

This problem was raised as issue #2.

This PR aims at fixing both problems by:

1. Moving the offending vowels = list(vowels) after the already existing special handling of r5.
2. Attaching any final retroflex with a regular expression.

A diff between the results with and without the fix did not show any breaking cases.