Enhance string hash

This tackles both issues mentioned in #24:

1. It increases the base length from 30 to 36.
2. It uses the full sha1 hash instead of only half of it.

It avoids wasting to much characters by using base64 instead of hex encoding for the sha1 hash.
Replace constant in MonolingualTextHandler
Merge pull request #44 from wmde/stringhasher

Enhance string hash
Add TimeHandler and register it
Rewrite epoche calculation and add tests
Updated to use DBAL
Multiple calculation errors fixed
Moved calculation to DataValues/Time
Drop newDataValueFromValueField
Default getEqualityFieldValue to DataValue::getHash
Support more than one sort field
Remove singular method
Merge pull request #47 from wmde/sort-array

Support more than one sort field
Merge pull request #45 from wmde/hash-decode

[WIP] Drop newDataValueFromValueField
Merge pull request #46 from wmde/equality-hash

Default getEqualityFieldValue to DataValue::getHash
Merge branch 'master' into HEAD
Merge pull request #21 from wmde/timeHandler

Add TimeHandler
Update README.md
Add equality field roundtrip test
Reimplemented getEqualityFieldValue