Switch build-backend to poetry-core (#24)

* Switch build-backend to poetry-core

Use poetry-core rather than poetry in pyproject.toml.  The former
is recommended for PEP 517 builds as it brings a smaller subset
of poetry modules needed to perform the build without all
the dependencies of the poetry package manager.  This makes builds much
faster.

* Require poetry-core>=1.0.7

Co-authored-by: Felix Fontein <felix@fontein.de>

Co-authored-by: Felix Fontein <felix@fontein.de>

Author: mgorny

pyproject.toml

@@ -1,6 +1,6 @@
 [build-system]
-requires = ["poetry>=0.12"]
-build-backend = "poetry.masonry.api"
+requires = ["poetry-core>=1.0.7"]
+build-backend = "poetry.core.masonry.api"
 
 [tool.poetry]
 name = "ansible-pygments"