Merge pull request #23 from linkerlin/master

增强单元测试
add stop method to spider #24
Merge branch 'master' of github.com:code4craft/webmagic
#25 use URL api in UrlUtils.canonicalizeUrl()
fix null pointe exception #26
complete test cases
[maven-release-plugin] prepare release webmagic-parent-0.3.1
[maven-release-plugin] prepare for next development iteration
update samples version
update version
update version
fix thread pool
fix a thread pool exception
add type convert
change formatter to class
some bugfix
add example
fix a test error
[maven-release-plugin] prepare release webmagic-0.3.2
[maven-release-plugin] prepare for next development iteration