Add specs docs and refactor (#70)

* Changed old style specs to more up to date specs

* Added documentation

* Changed all @spec to -spec's

* Bump version number

src/esqlite.app.src

@@ -1,7 +1,7 @@
 {application, esqlite,
  [
   {description, "sqlite nif interface"},
-  {vsn, "0.5.0"},
+  {vsn, "0.5.1"},
   {modules, [esqlite3, esqlite3_nif]},
   {registered, []},
   {licenses, ["Apache"]},