Package dependency resolution

[dahlia]

We need package metadata format to describe its dependencies e.g.

# countries/package.toml
[targets.python]
name = "countries"
[docs]
url = "https://spoqa.github.io/countries.nrm/"

# languages/package.toml
[targets.java]
name = "languages"
[docs]
url = "https://hongminhee.org/languages/docs/"

# currency/package.toml
[dependencies]
"https://github.com/spoqa/countries.nrm" = ">= 1.0.0, < 1.1.0"
"https://hongminhee.org/languages/" = ">= 1.0.0, < 1.1.0"
[targets.python]
name = "currencies"
vendors = ["https://hongminhee.org/languages/"]

Package dependencies should go to dependencies of the target package’s metadata e.g.:

# setup.py
setup(
    name='currencies',
    packages=['currencies', 'languages'],
    install_requires=[
        'countries >= 1.0.0, < 1.1.0',
        # 'languages'  # error on install
    ]
)

Or it should be possible to vendor some of its dependencies if these do not have the same target.