retry connection error delay

retry connection error delay

* improved ResultSet.items() performance

* now support python 2.6

* python 2.6 support fixes

* if_not_exists option for create_database
* new get_list_servers() method
* make use of urlparse to parse netloc
* fixed issue for creating/dropping numeric-named databases
* added healing feature on InfluxClusterClient
* made InfluxDBClusterClient thread-safe

* support for requests http(s) proxy

* python 3.5 compatibility fixes
* avoid mutable value for defaults of functions
* fixed switch_database for cluster client

* Added license to package

* Fix pandas FutureWarning

* Depend on six>=1.9.0

* Don't append 'i' to booleans

* Adapted to new line protocol: append a `i` to new integers

* Improved line protocol performance

* line protocol: handle None tags and fields
* line protocol: time precision support - timestamps that
  are send as integers are left intact but other timestamps
  are converted depending on the time precision
* line protocol: Handle field string values with several newlines