Add support to unserialize PHP sessions

[Xathz]

PHP sessions use a slightly different serialization:

session_expire_at|i:1597336404;last_seen_at_update|i:1596731654;loggedin|b:1;id|i:1000;manager_id|i:102;created_at|s:19:"2020-03-11 00:30:06";restricted|b:0;username|s:5:"exampleuser";display_name|s:5:"Example User";

Trying to unserialize as is gives Error: Syntax Error at index 2 while unserializing payload.

Maybe put this functionality under unserializeSession like some other libraries do. The existing libraries that support this are out of date and contain various breaking bugs :/