Updates on setup.py and sub-module definition

[gefei-qian-nih]

There are two places in setup.py that errored out. One is about checking gcc compiler name. Noe parameter is needed in _is_gcc() call. The other is on external library definition. libgmp was missed. This caused "memsurfer/_memsurfer_cmod.so: undefined symbol: __gmpq_add" error. These two parts are corrected in setup.py.

In the .sub-module defination, an https link is used for anonymous download.

Instruction is provided to install dependencies with conda.