Implement basic circle stamping (#53)

Cargo.lock

@@ -49,7 +49,6 @@ name = "graphite-document-core"
 version = "0.1.0"
 dependencies = [
  "kurbo",
- "svg_fmt",
 ]
 
 [[package]]
@@ -132,12 +131,6 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ea6a9290e3c9cf0f18145ef7ffa62d68ee0bf5fcd651017e586dc7fd5da448c2"
 
-[[package]]
-name = "svg_fmt"
-version = "0.4.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8fb1df15f412ee2e9dfc1c504260fa695c1c3f10fe9f4a6ee2d2184d7d6450e2"
-
 [[package]]
 name = "syn"
 version = "1.0.64"