fix(TestDeps): support go v1.16 (#52)

* fix(TestDeps): support go v1.16

* chore(gh/workflows): update to go 1.16

Fix panic on init failure like conflicting import

Support for merging multiple config files from variable (#43)

To better support the use-case of dynamically generating configs from other configs and variables, the following changes are made:

- Added `paths` to `file` config source. Either the existing `path` or `paths` is required.
   - All the files listed in `paths` are merged using `mergo` with `mergo.WithOverride` and `mergo.WithOverwriteWithEmptyValue`
- config source's `paths` and `path` can now refer to `var`s. `variant` internally builds a DAG of `var`s, `conf`s, and `sec`s to make it possible.
- Added `function` block to define user-functions, with support for recursive call. Note that user-functions are visible within a variant command that defines it.
  - This means two things:
    - You can't `import` user-functions
    - User-functions defined in the parent variant command are not visible to imported variant commands.
- Added new example for config-depends-on-var use-case at `examples/advanced/dynamic-config-inheritance`
- Added new example for importing variant command with local user-function at `examples/advanced/userfunc-local-scope`

Resolves #42

Use the same version of sdk as variant for `variant export` (#41)

This changes the build and release scripts to embed the version number of variant deduced from GITHUB_REF in GitHub Actions, and enhances `variant export` to embed that version in generated go.mod files.

Fixes #36

Fix regression in the test framework

Merge pull request #35 from mumoshu/run-as-k8s-controller

feat: Run Variant command as Kubernetes controller

Merge configs by overriding with empty values (#34)

Upgrades mergo to the version that has support for the WithOverwriteWithEmptyValue option that enables merging non-empty values in the destination config with empty values from the source config.

Fixes #33

Merge pull request #32 from mumoshu/embed-imports

Embed local imports and cached remote imports into binary

Merge pull request #30 from mumoshu/pass-globals-to-imported-jobs

Pass globals to imported jobs

Merge pull request #27 from mumoshu/fix-imports-not-importing-sub-jobs

Fix import/imports not importing non-top-level jobs via shebang