Fixed pom.xml file.

- Updated maven-compiler-plugin version from 2.3.2 to 3.1.
- Updated maven-gpg-plugin version from 1.0-alpha-4 to 1.4.
- Removed build-helper-maven-plugin declaration. Instead, the
  sourceDirectory tag is used to specify where the sources are.
Fixed permissions on files.

Removed executable bit from HashMap.java, CheckHashMap.scala and pom.xml
Widened generic type parameters.

Widened generic type parameters for some of the constructor methods.