Added possilility to use pool of SandCastles.

Pool-object is a drop-in-replacement for SandCastle-object. It runs
scripts on a pool of SandCastle-instances.

Only one script is allowed to run at a time on a single instance. This
is enforced by a queue system.
Fixed test.
Added possibility to use JavaScript strict mode, when running scripts.
Fixed 'pool should run scripts on non blocking instances'-test timeout.
Added memory limit for sandbox process.

Added possibility to limit memory usage of v8-instance on sandbox
process.
Fixed indentation problem caused by previous commit.