Use an allowlist-based .npmignore file (#250)

Reconcile the package.json "files" field and .npmignore into the
.npmignore file. Like package.json "files", an allowlist approach is
used by first ignoring everything (with `/*`) and then listing the
patterns that should be published using inverted patterns using the
leading `!`. After, filter out nested paths for tests to avoid
publishing such unnecessary files.
Note that the leading "**/" for tests is necessary as otherwise test
files would still be published (this was manually verified).

The previous approach, using both "files" and .npmignore, does not work
and only the "files" value was respected (this can be seen from the
files present in v4.2.0). It appears only one of the two can be used,
though I was unable to find a statement in the npm docs that say this
explicitly.

An alternative to the approach taken here would be to increase the
specificity of file patterns in the "files" array to avoid including
test files.

.npmignore

@@ -1,3 +1,16 @@
-__tests__/
-__stories__/
+# Ignore everything...
+/*
+
+# Except what needs to be published
+!/src
+!/lib
+!register.js
+!package.json
+!CHANGELOG.md
+!LICENSE
+!README.md
+
+# Unless it's tests
+**/__tests__/
+**/__stories__/
 *.test.{js,ts,tsx}

package.json

@@ -7,15 +7,6 @@
   "author": "Jonas Kello",
   "license": "MIT",
   "repository": "https://github.com/dividab/tsconfig-paths",
-  "files": [
-    "/src",
-    "/lib",
-    "register.js",
-    "package.json",
-    "CHANGELOG.md",
-    "LICENSE",
-    "README.md"
-  ],
   "engines": {
     "node": ">=6"
   },