Fix get_lib_name crashing on missing name

`Cargo.toml` manifests do not have to explicitly declare a `name` in the `[lib]` section of a library, but use a slugified version of the `[package]` name. This commit make it so `setuptools_rust` no longer crashes on such manifests.

Author: althonos

setuptools_rust/extension.py

@@ -101,7 +101,9 @@ def __init__(self, target, path,
     def get_lib_name(self):
         cfg = configparser.ConfigParser()
         cfg.read(self.path)
-        return cfg.get('lib', 'name').strip('"')
+        section = 'lib' if cfg.has_option('lib', 'name') else 'package'
+        name = cfg.get(section, 'name').strip('"')
+        return name.replace('-', '_').replace('.', '_')
 
     def get_rust_version(self):
         if self.rust_version is None: