Add --Location to curl command

When the package download link contains redirection, we need to add
--Location option to curl command.
Merge branch 'master' of https://github.com/dongli/packman
Add update subcommand
Replace incompatible sed command with perl

The sed commands in Linux and Mac are different, so I use perl instead.
Defer $fortran_compiler in install_root

To change package installation with different Fortran compilers easily,
I defer the '$fortran_compiler' in <package>_install_root, so when
source the bashrc, correct fortran_compiler can be used.