Updated Scalastyle to release 0.4.0.
Updated Scalastyle configuration.
Removed commented-out reference to Scalastyle.
Refactored SBT build to enable Scalastyle for multiprojects.

Scalastyle settings must be inherited by each project in order to
function correctly. The SBT Scala build script now utilizes a hierarchy
of settings such that scalastyle is enabled for subprojects.
Removed trailing whitespace.
Removed redundant braces to conform to Scalastyle rules.
Ignored Scalastyle error on casting of argument types.

There's currently no alternative to an explicit cast for the argument
type.
Refactored to simplify requireFinite.

The primary motivation was to overcome issues flagged by Scalastyle.
Also removed redundant "final" method qualifiers.
Committed file missing from prior commit.

Tests updated to reflect simplified requireFinite macro.
Refactored requireXXX macro string resource keys into constants.

Using named constants helps ensure consistency and avoids Scalastyle
complaining about their use within files.
Temporarily disabled the HeaderMatchesChecker.

This checker is currently not functioning correctly. Refer to
https://github.com/scalastyle/scalastyle/issues/84 for further
information.
Minor code reformatting.
Corrected header test so that it matches successfully.
Removed comments relating the the non-issue.
Corrected case in name of Scalastyle plugin.
Refactored sbteclipse plugin into a separate file.
Updated sbteclipse plugin to version 2.4.0.
Refactored name of sbteclipse plugin.
Refactored sbt-git plugin into separate file.
Refactored sbt-pgp plugin into a separate file.