Increased the number of variables that can be exported from 20 to the maximum of 100

[nicoboss]

Increased the number of variables that can be exported from the default value of 20 to 100 which is the maximum possible using a single API call. This fixes #15 but still doesn't address the missing pagination and so will result in a new hard limit at 100. At least it makes it possible to export 5 times more variables than before which should be enough for the majority of projects.