Find cereal, ELPA, FFTW3, ScaLAPACK in CMake.

[shishaochen]

In response to #50, this version automatically searchs dependencies from system default include/library paths.
Below is possible log when executing cmake ../cmake.

-- The CXX compiler identification is GNU 8.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found Boost: /usr/include (found version "1.67.0")
-- Found Cereal: /usr/local/include
-- Looking for sgemm_
-- Looking for sgemm_ - not found
-- Looking for C++ include pthread.h
-- Looking for C++ include pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE
-- Looking for sgemm_
-- Looking for sgemm_ - found
-- Found BLAS: /usr/local/lib/libopenblas.so
-- Found ELPA: /usr/local/lib/libelpa.so
-- Found ScaLAPACK: /usr/local/lib/libscalapack.a
-- Found FFTW3: /usr/local/lib/libfftw3.a
-- Found MPI_CXX: /usr/lib/x86_64-linux-gnu/libmpichcxx.so (found version "3.1")
-- Found MPI: TRUE (found version "3.1")
-- Found OpenMP_CXX: -fopenmp (found version "4.5")
-- Found OpenMP: TRUE (found version "4.5")
-- Configuring done
-- Generating done
-- Build files have been written to: /root/abacus-develop/ABACUS.develop/build