Port toml-test to pure Go (#264)

* Port toml-test to pure Go

This change basically ports the toml-test examples test suite to pure
Go. This removes the snowflake test.sh required to run such tests, and
allows us to the example tests on any platform (which includes Windows
as part of the pull-request testing).

* Allow CircleCI failure for go tip

.circleci/config.yml

@@ -27,6 +27,9 @@ commands:
             coverage:
                 default: false
                 type: boolean
+            allow_fail:
+                type: boolean
+                default: false
         steps:
             - run:
                 name: "Run tests for <<parameters.test_name>>"
@@ -36,13 +39,16 @@ commands:
                     trap "go-junit-report </tmp/test-results/go-test.out > ${TEST_DIR}/go-test-report.xml" EXIT
                     go test <<parameters.module>> -race -v \
                         <<# parameters.coverage >>-coverprofile=/tmp/workspace/coverage.txt -covermode=atomic<</ parameters.coverage >> \
-                        | tee /tmp/test-results/go-test.out
+                        | tee /tmp/test-results/go-test.out <<# parameters.allow_fail >>|| true<</ parameters.allow_fail >>
 
 jobs:
     go:
         parameters:
             version:
                 type: string
+            allow_fail:
+                type: boolean
+                default: false
         executor:
             name: golang
             version: "<<parameters.version>>"
@@ -50,21 +56,25 @@ jobs:
         steps:
             - checkout
             - run: mkdir -p /tmp/workspace
-            - run: go fmt ./...
+            - run: go fmt ./... <<# parameters.allow_fail >>|| true<</ parameters.allow_fail >>
             - get_deps
             - run_test:
                 test_name: "go-toml"
                 module: "github.com/pelletier/go-toml"
                 coverage: true
+                allow_fail: <<parameters.allow_fail>>
             - run_test:
                 test_name: "tomljson"
                 module: "github.com/pelletier/go-toml/cmd/tomljson"
+                allow_fail: <<parameters.allow_fail>>
             - run_test:
                 test_name: "tomll"
                 module: "github.com/pelletier/go-toml/cmd/tomll"
+                allow_fail: <<parameters.allow_fail>>
             - run_test:
                 test_name: "query"
                 module: "github.com/pelletier/go-toml/query"
+                allow_fail: <<parameters.allow_fail>>
             - store_test_results:
                 path: /tmp/test-results
     codecov:
@@ -103,6 +113,7 @@ workflows:
             - go:
                 name: "gotip"
                 version: "1.12" # use as base
+                allow_fail: true
                 pre-steps:
                     - restore_cache:
                         keys: