a complete gogrep rewrite (#221)

Reasons for the rewrite:

* Intended to be tightly integrated into ruleguard
* Better performance
* More library-oriented design
* Fixed some bugs

.github/workflows/go.yml

@@ -8,9 +8,9 @@
       "runs-on": "ubuntu-latest",
       steps: [
         {
-          name: "Set up Go 1.14",
+          name: "Set up Go 1.16",
           uses: "actions/setup-go@v1",
-          "with": {"go-version": 1.14},
+          "with": {"go-version": 1.16},
           id: "go",
         },
         {name: "Check out code into the Go module directory", uses: "actions/checkout@v1"},

go.mod

@@ -3,6 +3,7 @@ module github.com/quasilyte/go-ruleguard
 go 1.15
 
 require (
+	github.com/go-toolsmith/astequal v1.0.0
 	github.com/google/go-cmp v0.5.2
 	github.com/quasilyte/go-ruleguard/dsl v0.3.1
 	github.com/quasilyte/go-ruleguard/rules v0.0.0-20210203162857-b223e0831f88

go.sum

@@ -1,3 +1,5 @@
+github.com/go-toolsmith/astequal v1.0.0 h1:4zxD8j3JRFNyLN46lodQuqz3xdKSrur7U/sr0SDS/gQ=
+github.com/go-toolsmith/astequal v1.0.0/go.mod h1:H+xSiq0+LtiDC11+h1G32h7Of5O3CYFJ99GVbS5lDKY=
 github.com/google/go-cmp v0.5.2 h1:X2ev0eStA3AbceY54o37/0PQ/UWqKEiiO2dKL5OPaFM=
 github.com/google/go-cmp v0.5.2/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/quasilyte/go-ruleguard v0.3.1-0.20210203134552-1b5a410e1cc8/go.mod h1:KsAh3x0e7Fkpgs+Q9pNLS5XpFSvYCEVl5gP9Pp1xp30=