Deduper

Changed
* update requirements

Added
* [DOCS]: installation-linker.md

Changed
* [HASHER] - improved error checking
* [HASHER] - removed hack for PyInstaller

Changed
* [HASHER]: remove dependency on `log` object (Andrei Sura)
* [DOCS]: updates

Added
* [SCRIPTS]: save helper used before running the linkage (Andrei Sura)

Fixed
* [LINKER]: fix py36 issue due unpicklable SQLAlchemy `engine` (Andrei Sura)
* [HASHER]: fix py36 issue with `mp.get_log()` (Andrei Sura)

Changed
* [LINKER]: implement TODO about returning links (Andrei Sura)
* [LINKER]: make it use mp (Andrei Sura)
* [LINKER]: implement support for marking rows with `FLAG_SKIP_MATCH` when the lookup finds a link with the same hash from the same partner (Andrei Sura)
* [Travis CI]: add `dist: trusty` due EOL for Ubuntu Precise 12.04 (Andrei Sura)
* [README]: add links to the NIST pages about sha256 (Andrei Sura)
* [VALIDATION]: save helper script used for FP/FN calculation (Andrei Sura)
* [SCHEMA]: save the queries used for validation (Andrei Sura)
* [HASHER]: ask for confirmation before starting the process (Andrei Sura)

Fixed
* [BUG]: used `ahash_1` instead of `ahash_2` variable

Added
* draft installation steps for restricted windows

Changed
* [hasher]: make it faster using mp + introduced dependency on `dill` package
* [hasher]: implement the `missing values` rule for RACE and SEX if value in ['NI', 'UN', 'OT'] ==> no hash is generated

* [linker]: create a UUID even for patients with zero hashes
* Allow nulls in the `linkage_hash` column since some patients do not have all required data elements
* [schema]: update linkage table with `rule_id` + `fk_linkage_rule_id`
* [linker]: fix error with un-set flag + do not create tables using SQLAlchemy
* [linker]: update example config file file
* logging: search the config file under `cwd`
* Split requirements into two to reduce dependencies for pypi installs
* [linker]: add logic for logging hashes that resolve to two distinct UUIDs
* [linker]: update schema definition for UUID use varchar(32) instead of binary(16)
* [linker]: changed the model to use a `text` field for UUIDs instead of `binary` (for compatibility with the PCORI tables)
* [linker]: when there is only one hash provided store the link object in the proper slot
+ return a link when hashes resolve to two different UUID's

* [linker]: implement 2 changes per Jiang - if only one of the two hashes is found re-use existing UUID
(previously we were giving precedence to the `rule_1` hash by generating a new UUID)

Changed
* consider race=07 (refused to answer) the same as UN, thus not generating a hash for rules involving this race value (Jiang Bian)