Override sizeThatFits instead of sizeToFit

* Should not override sizeToFit according to Apple's doc.
Customisable colors (#57)
Issue #46
Use instancetype
Fixed Issue #58
Merge pull request #53 from krafttuc/fix-token-size

Override sizeThatFits instead of sizeToFit
Stuff
Fix placeholder bug that remained hidden although it should has been shown. The following cases have been covered.
1. No tokens - enter text  and delete text
2. One token - delete token
Merge pull request #64 from mrvincenzo/master

Fix placeholder bug that remained hidden although it should has been shown
Clean up
fix for #61. No reason to shift focus to tokenField
Handle transparent navigation bar in ios7. Fixes #62
Merge pull request #65 from nagrao/ios7

fix for #61. No reason to shift focus to tokenField
Making sort of results optional

For some result sets we may not need the sorting of results. Making
it configurable so that caller can decide if it needs sorting. This
is particularly useful for default implementation as it performs
a brute force search on the source array which can be sorted once
by the caller and used thereafter as it is without cost of sorting
it everytime.
Allowing search in background thread

Allowing caller to set flag to search in background. This is
particularly useful when we have a long source array in which
we are going to search, which can potentially lead to blocking
of main thread for a long time.

Have tested it in the example by setting this flag to both YES
and NO. To maintain backward compatiblity just keeping the default
value to NO.
Merge pull request #70 from manveer/master

Adding search in background thread
only add tokens of didBeginEditing if they were removed on didEndEditing
Merge pull request #75 from mng12689/fix_didBeginEditing_behavior

only add tokens of didBeginEditing if they were removed on didEndEditing
Add custom search algorithm option in the delegate
Merge pull request #77 from jmig/custom-search

Custom search option to the delegate