.base_url               Return base url of Airly API v2
.get_apikey             Get Airly apikey
.send_request           Sends a request to the specified url and
                        retrieves it's content.
add_json_extension      Adds the json extension to the given url
add_path                Adds the given path to the given url
assert                  Asserts a given expression and throws an error
                        if it returns FALSE
assert_apikey           Checks whether apikey is correctly set
assert_coordinates      Checks whether apikey is correctly set
assert_ids              Checks whether ids are correctly defined. If
                        not throws an error
build_current_df        Creates an object representing Airly
                        measurement
build_forecast_df       Creates object containing information about
                        history data for given API response
build_history_df        Creates object containing information about
                        history data for given API response
create_airly_api_response
                        Creates an object representing a response from
                        the Airly API. Also every API call return
                        information about current limits What is used
                        to assign variables in pkg.env
create_airly_location   Creates an object representing Airly location
create_airly_measurement
                        Creates an object representing Airly
                        measurement
create_airly_meta       Creates a data.frame representing Airly meta
create_request_url      Creates a request url based on the given base
                        url and passed paths. The json extensions is
                        added automatically.
get_content             Retrieves the response content
get_indexes             Get Airly available indexes
get_installation_by_id
                        Get Airly installation by id
get_installation_measurements
                        Get Airly measurements for any geographical
                        location given installation id
get_measurements_info   Get measures used in Airly
get_nearest_installations
                        Get Airly nearest installations to given point
get_nearest_measurements
                        Get Airly nearest measurements to given point
get_point_measurements
                        Get Airly measurements for any geographical
                        location
is_airly_api_response   Checks whether the given object is of the class
                        airly_api_response
is_airly_location       Checks whether the given object is of the class
                        airly_location
is_airly_measurement    Checks whether the given object is of the class
                        airly_measurement
parse_json              Parses a json response
print.airly_measurement
                        Print for "airly_measurement" type objects
remaining_requests      Get information about remaining API requests
replace_null            Replaces NULL with NA for nested lists. Useful
                        when NULL value leads to error while object
                        casting
set_apikey              Set Airly apikey
validate_airly_api_response
                        Checks if the given response is not empty and
                        that it did not return an error http code.
validate_airly_location
                        Checks whether the given object is correctly
                        defined airly_location class
validate_airly_measurement
                        Checks whether the given object is correctly
                        defined airly_measurement class
validate_airly_meta     Checks whether the given object is correctly
                        correctly defined
