Use `http_build_query()` to improve readability and reduce risk of errors.

Use GET instead of POST to better match the verb to the request and for consistency between downloaders.

Changed:
- Throw `InvalidArgumentException` instead of `UnexpectedValueException` when dealing with an unsupported package in Ninja Forms, PublishPress Pro, and WPML.
- Throw `UnexpectedValueException` if the decoded/unserialized API response is not an array.
- Improved messages to clarify errors from API.
- Fixed and improved PHPDoc tags to document exceptions.

Changed:
- Use booleans intead of integers for cURL options.
- Compile URL in GET request earlier to organize cURL options similarly to POST request.

Changed:
- Added protected method `request()` to aggregate the execution of the request, handling of the response, and closing of the cURL handler.
- Added cURL option `CURLOPT_FAILONERROR` to fail if the response is >= 400.
- Throw `RuntimeException ` if the request failed.
- Fixed and improved PHPDoc tags.

Changed:
- Replaced `getDownloadUrl()` in EDD plugins with a new protected method `getDownloadUrlFromApi()` that only handles the request for the download URL response object.
- Replaced `extractDownloadUrl()` with `getDownloadUrl()` in `AbstractEddPlugin` that retrieves the response to parse from the plugin's `getDownloadUrlFromApi()`.
- Wrapped requests with `Http` in a try/catch to intercept cURL exceptions and wrap them in a plugin-aware exception.

A URL is necessary for requests.

Changed:
- Removed extraneous property descriptions.
- Rephrased description of `$slug` property to be more specific.
- Added missing `$slug` method parameter.

Amends cee1cf5

Accidentally reverted back from GET to POST.

Decoupled API URL and API URL query parameters from its HTTP query building and URL concatenation, and HTTP request call.

This allows the base URL and query parameters to be more readable from their final concatenated URL or HTTP request call.

This ensures compatibility with the classes' `$version` property being potentially empty, presuming a request for the latest version.

To reduce repetition, and risk of mistakes, when formatting the plugin's Composer package name. The package name is used in the messaging of most exceptions thrown.

Storing vendor name as a namespace

Changed:
- Moved shared cURL options to `request()` method.
- Catch any exception from `Http` requests.

Separated JSON decoding error handling from HTTP request/response error handling.

By using `json_last_error()`, we can provide a more precise error for end users as opposed to just checking if its an array.

Output a truncated excerpt of the response body if JSON decoding fails to give a hint of what the issue might be.

Separated unserialization error handling from HTTP request/response error handling.

Wrapped unserialization in try/catch to intercept any throwables from unexpected objects in their unserialization handlers. Gravity Forms is supposed to return an associative array but could be compromised.

Output a truncated excerpt of the response body if unserialization fails to give a hint of what the issue might be. Ideally, add an error handler to catch the PHP notice that is raised by `unserialize()`.