Can't change the slave MBUS channel id's without a library modification

[jicho]

Hi,

I have a new gasmeter that is not installed on MBUS channel 1, but on channel 2. As a result I did not get any gasmeter values.

Is it possible to add some sort of configuration to the library so users of this lib don't need to make changes in the library to get, for example, gasmeter data from the correct channel?

In other words... Make is easier to change the following values without the need to make library changes:

const uint8_t GAS_MBUS_ID = 1;
const uint8_t WATER_MBUS_ID = 2;
const uint8_t THERMAL_MBUS_ID = 3;
const uint8_t SLAVE_MBUS_ID = 4;

In the end a solution would be a nice addition for this project:
https://github.com/mrWheel/DSMRlogger2HTTP