DOCS: add issue user manual.
pullrequest: removed unused variable
removed unused method
PullRequest: Improve performance by reusing of result.

Reuse the result of PulllRequestComment.hadValidCommitId and
PullRequestComment.isCommitLost.
PullRequest: Apply tail recursion to partial_comments

* Split partial_comments into TemplateHelper.scala and three templates.
* Apply tail recursion.
PullRequest: Apply tail recursion to threadAndRemains

This prevents possible stackoverflow.
pullrequest: restore mergeCommitIdTo
Merged pull request from whiteship/yobi

http://yobi.navercorp.com:80/dlab/hive/pullRequest/276
pullrequest: restore mergeCommitIdTo
MergeCommitIdTo를 설정하는 코드를 원래 코드로 다시 돌립니다.
Merged pull request from whiteship/yobi

http://yobi.navercorp.com:80/dlab/hive/pullRequest/274
pullrequest: removed unused variable
`activeTab`이라는 변수를 더이상 사용하지 않기 때문에 삭제합니다.
code: parse object id to get a commit object
docs: Every source file should end with a newline

It breaks some rules of some standards:
* In section 2.1.1.2 of the ANSI C 1989 standard, "A source file that
  is not empty shall end in a new-line character, which shall not be
  immediately preceded by a backslash character."
* Posix defines a line as "A sequence of zero or more non- <newline>
  characters plus a terminating <newline> character." in
  http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_206

If you omit a newline character at end of file:
* git, gcc and vim may warn about that.
* wc does not count the last line as a line.
removed unneccessary locking
PullRequest: Make renderRawFile 40% faster by StringBuilder
MomentUtil: Compile the script engine only once.

Reuse script engine if it is already compiled.
PulllRequest: Reuse merged repository for performance.

Getting an object from repository has been being slow because of reading
pack index.
PullRequest: Remove unnecessary comment header.
Merged pull request from whiteship/yobi

http://yobi.navercorp.com:80/dlab/hive/pullRequest/279
removed unneccessary locking
```
        GitRepository.cloneAndFetch(pullRequest, new AfterCloneAndFetchOperation() {
```

I removed the synchronization code in the callback, `AfterCloneAndFetchOperation`, because It is already in a synchronization started by `cloneAndFetch` method.

```
public static synchronized void cloneAndFetch(PullRequest pullRequest, AfterCloneAndFetchOperation operation) {
```
Merged pull request from npcode/yobi

http://yobi.navercorp.com:80/dlab/hive/pullRequest/254
PullRequest 댓글 렌더링 성능 많이 개선
PullRequest: Remove unnecessary comment header. (이것은 성능개선만을 위한 것은 아니고 #528도 고칩니다)
PulllRequest: Reuse merged repository for performance. (이것만으로 20% 이상의 성능 개선 효과 있음)
MomentUtil: Compile the script engine only once. (개선효과는 5% 정도)
PullRequest: Make renderRawFile 40% faster by StringBuffer (코드가 지저분해지는 단점은 있음. 개선효과는 1~5% 정도)
PullRequest: Apply tail recursion to threadAndRemains (이것은 성능개선 효과는 크지 않으나, tail recursion을 적용해서 stackoverflow의 가능성을 예방함)
PullRequest: Apply tail recursion to partial_comments (개선효과는 15% 정도)
PullRequest: Improve performance by reusing of result. (개선효과 측정안됨. 필요없을지도)

3배 정도 빨라질 것입니다.
Merged pull request from npcode/yobi

http://yobi.navercorp.com:80/dlab/hive/pullRequest/278
docs: Every source file should end with a newline
It breaks some rules of some standards:
* In section 2.1.1.2 of the ANSI C 1989 standard, "A source file that
  is not empty shall end in a new-line character, which shall not be
  immediately preceded by a backslash character."
* Posix defines a line as "A sequence of zero or more non- <newline>
  characters plus a terminating <newline> character." in
  http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_206

If you omit a newline character at end of file:
* git, gcc and vim may warn about that.
* wc does not count the last line as a line.
Merged pull request from kjkmadness/yobi

http://yobi.navercorp.com:80/dlab/hive/pullRequest/277
code: parse object id to get a commit object
To get a commit object, parse the object id.
Don't use object id as commit id.