Many-Core Engine for Perl providing parallel processing capabilities

Changes for 1.889

• Add Android support. Thank you, Dimitrios Kechagias.
• Revert defer signal-handling in MCE::Channel (send2 method).
• Improve mutex synchronize (aka enter) with guard capability. Thank you, José Joaquín Atria.
• Fix mutex re-entrant lock on the Windows platform.
• Add mutex guard_lock method.