Merge branch 'release/0.0.80' into develop
src: add class 'is_eigen_fullpivlu' for the member function 'is_square_matrix' of template class base
src: add instance method 'determinant()'
test: add instance method 'determinant()' testings
lint: add some files for linting pass
src: modify some code for linting pass
readme: add instance method 'determinant()' api for FullPivLU and CFullPivLU

fix a mistake
readme: improve the readability
npm: 0.0.80 -> 0.0.81
Merge branch 'release/0.0.81'