Make installable with meson

[awvwgk]

Thanks for this really nice project. I had a quick look over the meson build files and noticed that it was not installable, this patch makes your project install smoothly in way that it can be used from meson, CMake, autotools and co.

Changes:

• use library instead of shared_library
• prefer -Ddefault_library=shared in project default_options
• install module files in <includedir>/fazang
• generate pkg-config export and install in <libdir>/pkgconf
• declare dependency for subproject use
• rename source files from .f90 to .F90 to not require explicit -cpp options

This allows other meson projects to use your library with:

fazang_dep = dependency('fazang', fallback: ['fazang', 'fazang_dep'])

and either find an installed version via pkg-config or build it as subproject on demand via a wrap file (subprojects/fazang.wrap):

[wrap-git]
directory = fazang
url = https://github.com/yizhang-yiz/fazang
revision = head

[yizhang-yiz]

Thanks a lot!