Simplify parse and stringify methods

[Yeti-or]

original: bem/bem-sdk#181

Atm naming has shared parts of code with BemEntityName like usage of deprecated fields.
Would be better to has a tiny method for stringifying entityName with naming:

let res = e.block;
e.elem && (res += delims.elem + e.elem);
e.mod && (
  res += delims.mod.name + e.mod.name,
  e.mod.val === true || (res += delims.mod.val + e.mod.val)
);
return res;

and another tiny method for normalization old versions to the modern one as it does in BemEntityName.create: https://github.com/bem-sdk/bem-entity-name/blob/86e59d24/lib/entity-name.js#L379-L406

Perhaps we can make a separate function to let users use it with stringify as they did it before.