Remove 'build' directory

As the "build" dfirectory is picked up by the top-level build rule,
the two test executables are added to the build. The explicit target
property "\<asynch-exceptions\>on" and the dependency on Boost.System
(via Boost.Timer -\> Boost.Chrono) leads to conflicting target types
when building named libraries for staging.
The error message is:

error: Name clash for '\<pE:\\dev\\devel\\boost\\stage\\lib\>libboost_system-vc120-mt-1_57.lib'
error: 
error: Tried to build the target twice, with property sets having 
error: these incompabile properties:
error: 
error:     -  \<asynch-exceptions\>off
error:     -  \<asynch-exceptions\>on
error: 
error: Please make sure to have consistent requirements for these 
error: properties everywhere in your project, especially for install
error: targets.

The proposed solution is to move the build rules to the test directory
and making them "explicit" as to not interfere with the testing
system. Another solution would be to move the tests to a separete
"benchmark" directory.