Drop PHP 5.x

[Hywan]

See #74 for more information.

Progression

Library	PR	Tests are green	Merged
Acl	✅	✅	❌
Bench	✅	✅	❌
Cli	✅	✅	✅
Compiler	✅	✅	❌
Consistency	✅	❌	✅
Console	✅	✅	✅
Database	✅	✅	❌
Devtools	❌	❌	❌
Dispatcher	✅	✅	❌
Dns	✅	❌	❌
Event	✅	❌	✅
Eventsource	✅	❌	❌
Exception	✅	❌	✅
Fastcgi	✅	❌	❌
File	✅	✅	✅
Graph	❌	❌	❌
Heap	❌	❌	❌
Http	✅	✅	✅
Irc	✅	❌	❌
Iterator	✅	✅	✅
Json	✅	❌	✅
Locale	✅	✅	✅
Mail	✅	❌	❌
Math	✅	✅	✅
Mime	✅	✅	❌
Option	✅	✅	✅
Praspel	❌	❌	❌
Promise	✅	❌	❌
Protocol	✅	❌	✅
Realdom	❌	❌	❌
Regex	✅	❌	✅
Registry	✅	✅	❌
Router	❌	❌	❌
Ruler	❌	❌	❌
Session	❌	❌	❌
Socket	✅	✅	✅
Stream	✅	✅	✅
Stringbuffer	❌	❌	❌
Test	✅	✅	✅
Ustring	✅	✅	✅
View	✅	✅	✅
Visitor	✅	✅	✅
Websocket	✅	✅	✅
Worker	✅	❌	❌
Xml	❌	❌	❌
Xyl	❌	❌	❌
Zformat	❌	❌	❌
Zombie	✅	✅	❌

[Pierozi]

@Hywan Can I help there? Which repository should I focus?