feat: bump version to 0.2.0 and update changelog with release notes

Update WREN_VERSION_MINOR from 1 to 2 and WREN_VERSION_STRING from "0.1.0" to "0.2.0" in wren.h header. Add comprehensive 0.2.0 changelog entry documenting new language features (relative imports, Fiber value passing, String/Sequence/List/Num methods, Map iteration), C API additions (wren.hpp, user data, wrenAbortFiber), and CLI improvements (path module, --version flag, REPL, Platform class, process→os rename).

CHANGELOG.md

@@ -1,3 +1,44 @@
+## 0.2.0
+
+0.2.0 spans a pretty wide time period with [around 290 commits](https://github.com/wren-lang/wren/compare/0.1.0...master).
+This includes many bug fixes, improvements, clarity in the
+code and documentation and so on. There's too many to explicitly list.
+Below is the obvious user facing stuff that was easy to spot in the history.
+
+Most noteworthy is that 'relative imports' are a slightly breaking change,
+but help pave the way forward toward a consistency for modules.
+
+### Language/VM
+
+- `import` was made smarter, differentiating relative from logical
+- `Fiber` can now accept a value from the first `call`/`transfer`
+- Added `String.trim`, `String.trimEnd`, `String.trimStart` variants
+- Added `String.split`, `String.replace`, `String.fromByte`
+- Added `String.indexOf(needle, startIndex)`
+- Added `Sequence.take` and `Sequence.skip`
+- Added `List.filled(count, value)`
+- Added `Num.pow`, `Num.log`, `Num.round`
+- Added `Num.largest`, `Num.smallest`
+- Added `Map` iteration (`MapEntry`)
+
+#### C API
+
+- Added `wren.hpp` for use in c++
+- Added void* user data to `WrenVM`
+- Allow hosts with no module loader to still load optional modules.
+- Added `wrenAbortFiber`
+
+### CLI
+Please note that beyond 0.2.0 the CLI will have it's own changelog.
+This list is not exhaustive. For a fuller history see the commit log above.
+
+- Add path module
+- Add `--version`
+- Add REPL written in Wren
+- Add Stdin.isTerminal
+- Added Platform class
+- Rename `process` module to `os`
+
 ## 0.1.0
 
 First declared version. Everything is new!