Move deps and build to be less weirdly named and to condense placement of all build artifacts

.gitignore

@@ -1,8 +1,4 @@
-/_build/
-/cover/
-/deps/
-/doc/
+*.secret.exs
+/build
+/doc
 erl_crash.dump
-npm-debug.log
-/assets/node_modules/
-/config/*.secret.exs

mix.exs

@@ -1,6 +1,9 @@
 defmodule Lytedev.MixProject do
   use Mix.Project
 
+  @build_path "build"
+  @deps_path Path.join(@build_path, "deps")
+
   def project(), do: [
     app: :lytedev,
     version: "0.1.0",
@@ -9,6 +12,8 @@ defmodule Lytedev.MixProject do
     config_path: "src/config.exs",
     test_paths: ["src/test"],
     start_permanent: true,
+    build_path: @build_path,
+    deps_path: @deps_path,
     deps: deps()
   ]