Add GP Tuner and related doc (#1191)

* fix link err in docs

* add spaces

* re-organise links for detailed descriptions of the tuners and accessors; fix link err in HpoComparision.md

* add in-page link by change .md to .html

* delete #section from cross-file links to make links work in both readthedocs and github docs

* gp_tuner init from fmfn's repo

* fix params bug by adding float>int transition

* add optimal choices; support randint&quniform type; add doc

* refine doc and code

* change mnist yml comments

* typo fix

* fix val err

* fix minimize mode err

* add config test and Hpo result

* support quniform type; update doc; update test config

* update doc

* un-commit changed in yarn.lock

* fix optimize mode bug

* optimize mode

* optimize mode

* reset pylint, gitignore

* revert .gitignore yarn.lock

tools/nni_cmd/config_schema.py

@@ -104,6 +104,21 @@ tuner_schema_dict = {
             },
         Optional('gpuNum'): setNumberRange('gpuNum', int, 0, 99999),
     },
+    'GPTuner': {
+        'builtinTunerName': 'GPTuner',
+        'classArgs': {
+            Optional('optimize_mode'): setChoice('optimize_mode', 'maximize', 'minimize'),
+            Optional('utility'): setChoice('utility', 'ei', 'ucb', 'poi'),
+            Optional('kappa'): setType('kappa', float),
+            Optional('xi'): setType('xi', float),
+            Optional('nu'): setType('nu', float),
+            Optional('alpha'): setType('alpha', float),
+            Optional('cold_start_num'): setType('cold_start_num', int),
+            Optional('selection_num_warm_up'):  setType('selection_num_warm_up', int),
+            Optional('selection_num_starting_points'):  setType('selection_num_starting_points', int),
+            },
+        Optional('gpuNum'): setNumberRange('gpuNum', int, 0, 99999),
+    },
     'customized': {
         'codeDir': setPathCheck('codeDir'),
         'classFileName': setType('classFileName', str),