Avoid locking as much as possible related to Chronology caching.

All Chronology classes used synchronising on the chronology cache, which
leads to degraded performance once the cache has a high hit ratio.
This patch narrows the synchronised path onto the updating part by using
ConcurrentHashMap. The remaining synchronisation ensures identity and
prevents lost updates, which might be acceptable but are not strictly
backwards compatible.
Simplified Cache Lookup of GJChronologies.

This commit replaces the cache lookup using only the zone and then
iterating over the ArrayList donating possible candidates with a single
cache access. For this purpose a temporary cache key is instantiated.

In the cache hit case this code will produce a temporary GJCacheKey
object and then return the GJChronology, as compared to previous, where
the code was forced synchronised, an ArrayList iteration was performed
and an Instant was checked for equality.
only synchronize the write to STLYE_CACHE as the update will be atomic.
Using ConcurrentHashMaps rather than synchronized Maps.
using custom key for looking up from the StyleFormatter cache.

Previously a String was created from the ints, and a locale.toString was
invoked (which is a pretty heavy operation).
Now we use a custom key which is based on the same ints and locale, but
does not need to calculate a string out of it.
Update website and pom
Merge branch 'avoid_lock_contention_chonology_cache' of https://github.com/CodingFabian/joda-time into CodingFabian-avoid_lock_contention_chonology_cache
Increased performance of chrnology lookup

Fixes #126
Merge branch 'avoid_lock_contention_formatter_cache' of https://github.com/CodingFabian/joda-time into CodingFabian-avoid_lock_contention_formatter_cache
Adjust pull request to use AtomicReferenceArray

Fixes #129, #127
Update headers
Handle weird TimeZone implementations with null ID

Calling DateTimeZone.forTimeZone() would break if the ID was null
Fixes #133
Added missing words in ReadableDuration's javadoc
Removing incorrect 'equal to'
Merge pull request #137 from Strilanc/patch-1

Added missing words in ReadableDuration's javadoc
Fix Javadoc for ReadableDuration

See #137