Added use statement for MemoryCacheException

… negatives

…into benswinburne-fix-file-has

This was supported in 1.8, but missing in 2.0
Supports both the mongodb\mongodb library as the (legacy) mongo extension

Differenes from 1.8:
 - Constructor takes db and/or collection as arguments
 - Use `_id` field rather than custom `key` field
 - Expired items are ignored rather than deleted (just like Mysqli)
 - Using upsert rather than delete + insert
 - Store TTL as date bson type to allow ttl index

Includes unit tests.
Usage guide is added to README.

Fixes desarrolla2#25

APCU 5.x requires php7, therefor it pecl won't install it for version 5.x
This causes Travis to fail without running any tests

Fix pecl issue on Travis

Create default backend object is nothing is supplied

Added Mongo support.

List the available methods.
Fixes desarrolla2#29

List the available methods in README

Fixup for desarrolla2#30

Update README.md

Calling `getKey()` before passing the key to `getFileName()` from `getValueFromCache()` is not only unnecessary, it actually breaks caching if the prefix is not empty.
I discovered this from a slightly different perspective: in my application I had to inherit from `Adapter/File` and override `getKey()` so that it applies `sha1()` to it as I frequently get cache keys with colons and other garbage in them. So as with a non-empty prefix, the key gets mutated in this instance, and then gets mutated yet again by the second `getKey()` call, so the lookup key is actually completely different.

Remove duplicate invocation of getKey() in File::getValueFromCache()

Expired ttl test give Ecxeption

All cache adapters follow PSR-16
Removed Memcache (only support memcached ext)
Multi key get and set for supported adapters
Rely on service TTL where possible, no additional checks
Added FlatFile adapter for flat files. TTL is written in differnt file.
Removed the PackTtlTrait
Fixed NopPacker
Added PhpPacker, only to be used with files
Require all libs and extensions for development

Immutable
Move PHP from packed to PhpFile implementation
Multiple strategies for File cache
Use external PSR-16 test suite
PHP 7 only
multiple for Mongo
multiple for Predis
clear for File and PhpFile
Lots of fixes

Added class to using Trie directory structure

Moved options into trait
Better abstraction choises

Run travis on PHP 7.3

Removing this from README.md

[skip ci]

Fix tests for PHPFile cache

Closes desarrolla2#66

Fixed up name
Added MongoDBBinaryPacker

[skip ci]

…acker

Fixes bug in JsonPacker

upgrade