feat: builder api (#97)

* feat: replace createFormSchema with FormSchemaBuilder

* refactor: class based FormSchemaBuilder

* refactor: reorganize schema builder code

* refactor: reorganize create-form-validator code

* feat: replace createFormValidator with FormValidatorBuilder class

* docs: fix broken and outdated jsdocs for decoders

Co-authored-by: Mikołaj Klaman <mklaman@virtuslab.com>

README.md

@@ -46,26 +46,26 @@ npm install @virtuslab/formts
 #### 2) Define shape of the form
 
 ```ts
-import { createFormSchema } from "@virtuslab/formts";
+import { FormSchemaBuilder, FormFields } from "@virtuslab/formts";
 
-const Schema = createFormSchema(
-  fields => ({ answer: fields.string() }),
-  errors => errors<string>()
-);
+const Schema = new FormSchemaBuilder()
+  .fields({ answer: FormFields.string() })
+  .errors<string>()
+  .build();
 ```
 
 #### 3) Define validation rules (optional)
 
 ```ts
-import { createFormValidator } from "@virtuslab/formts";
+import { FormValidatorBuilder } from "@virtuslab/formts";
 
-const validator = createFormValidator(Schema, validate => [
-  validate(
+const validator = new FormValidatorBuilder(Schema)
+  .validate(
     Schema.answer,
     val => (val === "" ? "Required!" : null),
     val => (val !== "42" ? "Wrong answer!" : null)
-  ),
-]);
+  )
+  .build();
 ```
 
 #### 3) Create controller holding form state