upgrade PyO3 to 0.14

This fixes a build issue under PyPy:
#18

This raises the minimum support Python version to 3.6.

.github/workflows/maturin_build_wheel.py

@@ -19,7 +19,6 @@
 # for consistency.
 if platform.system() == "Linux":
     version_path_components = {
-        (3, 5): "cp35-cp35m",
         (3, 6): "cp36-cp36m",
         (3, 7): "cp37-cp37m",
         (3, 8): "cp38-cp38",

.github/workflows/push.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ${{ matrix.platform.os }}
     strategy:
       matrix:
-        python-version: [3.5, 3.6, 3.7, 3.8, 3.9] # This list needs to be kept in sync with tag.yml and maturin_build_wheel.py.
+        python-version: [3.6, 3.7, 3.8, 3.9] # This list needs to be kept in sync with tag.yml and maturin_build_wheel.py.
         rust-toolchain: [stable, beta, nightly]
         platform: [
           { os: "ubuntu-latest",  python-architecture: "x64", rust-target: "x86_64-unknown-linux-gnu" },

.github/workflows/tag.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.platform.os }}
     strategy:
       matrix:
-        python-version: [3.5, 3.6, 3.7, 3.8, 3.9] # This list needs to be kept in sync with push.yml and maturin_build_wheel.py.
+        python-version: [3.6, 3.7, 3.8, 3.9] # This list needs to be kept in sync with push.yml and maturin_build_wheel.py.
         platform: [
           { os: "ubuntu-latest",  python-architecture: "x64", rust-target: "x86_64-unknown-linux-gnu" },
           { os: "macOS-latest",   python-architecture: "x64", rust-target: "x86_64-apple-darwin" },

Cargo.toml

@@ -22,6 +22,6 @@ neon = ["blake3/neon"]
 
 [dependencies]
 blake3 = { version = "0.3.5", features = ["rayon"] }
-pyo3 = { version = "0.12", features = ["extension-module"] }
+pyo3 = { version = "0.14", features = ["extension-module"] }
 arrayref = "0.3.6"
 hex = "0.4.2"