IGRF13 Applied

The year of 2030 is the last one can be calculated now.

new coefficients in IGRF-13

update to IGRF-13. Result after 2010 may be different. The year of 2030 is the last one can be calculated now.

0.1.8

fix a bug about Linux file path

0.1.7

fix a bug about README.md

0.1.6: for using more flexible.

watch README.md

0.1.5

update README.md