implement detector to check implicit elements.
update metadata and README.
Merge branch 'master' into detect-implicit-length

Conflicts:
	README.md
	src/main/meta/bugrank.txt
	src/main/meta/findbugs.xml
	src/main/meta/messages.xml
refs #14: follow Mr.LI's suggestion.

https://github.com/WorksApplications/findbugs-plugin/pull/14#discussion_r6960545
refs #14: consider LOB type to support.
refs #14: consider StringBuffer as target type.
refs #14: fix and update test cases.
refs #14: @Lob might be annotated for BLOB.
refs #17: implement NullablePrimitiveDetector.
remove needless trailing spaces.
refs #14: correct wrong naming, thanks @wliyongfeng!
refs #14: explain why user should care about too long varchar column.
Merge pull request #14 from eller86/detect-implicit-length

Detect implicit 'length' and 'nullable' of @Column
Merge pull request #18 from eller86/nullable-primitive

Detector for nullable primitive