add bytecode cache (v 3.0.0)

* add function \PhpTags::getBytecode()
* add function \PhpTags::updateBytecodeCache()
* add function \PhpTags::clearBytecodeCache()

* add $wgHooks['OutputPageParserOutput'][] = 'PhpTags::updateBytecodeCache'
* add $wgHooks['ArticleDeleteComplete'][]	= 'PhpTags::clearBytecodeCache'
* add $wgHooks['PageContentSaveComplete'][]	= 'PhpTags::clearBytecodeCache'

* add $wgPhpTagsBytecodeExptime = 86400 * 30; // 30 days

Change-Id: Iaa03ad5dba19279bcea0f1c7942c3e041bb39793