[zh_cn] adjusts the transtation for PHP_Invoker in installation.xml.
[zh_cn] Sync with 3811b18

Added a note about installing Xdebug to the code coverage analysis chapter.
[zh_cn] sync with dfb8688
[zh_cn] sync with  f21eb76
[zh_cn] sync with bf35bbc
[zh_cn] sync with be7ad52
[zh_cn] sync with 470a0c5
[zh_cn] sync with 0283044

Documented `@coversDefaultClass`.
[zh_cn] sync with b3b2132d62d49da252f927764b0371631ec49130

Fixes #48
Documented strict mode.
[zh_cn] sync with 97d73319d5cd71a9b0410e9d04703332234f4fb9

Fixes #76
Documented the `callback()` constraint.