Provide a standalone infer function

[roll]

Overview

For now there is only one infer mention in readme. And it says:

You can instantiate a table object without schema, in this case the schema will be inferred automatically based on the data

$table = new Table("tests/fixtures/data.csv");
$table->schema()->fields();  // ["first_name" => StringField, "last_name" => StringField, "order" => IntegerField]

It useful (and often used in other languages) to have this functionality ALSO not related to the Table class e.g. as:

• Schema::infer

[OriHoch]

added in 3748750