v 1.3

1. Add the Nadaraya-Watson type kernel
2. Add the Priestley-Chao type kernel
3. Add the Gasser-Muller type kernel

v 1.2

1. Add the ker function to compute different types of kernel functions
2. Update some functions accordingly

v 1.1

1. Add the package dependency
2. Add the Gaussian error in the package title
3. Update the email address

v 1.0

1. Package has built