docs: comprehensive CHANGELOG update for all changes since v1.3.0

Updated CHANGELOG.md to include all merged PRs since version 1.3.0 (2020-02-13):

Added features:
- Jekyll Extensions Support (#114)
- Auto-Escape Feature (#111)
- Template Loader (#107)
- BasicEngine (#104)
- JSON Filter (#84)
- Strict Variables Mode (#74)
- Custom Writer Support (#86)
- Template AST Access (#59, #66)
- For-Else Support (#93)
- Unless-Else Support (#68)
- General Range Expressions (#65)
- Loop Modifier Expressions (#67)

Fixes:
- Size filter, slice bounds, division by zero
- Nil pointer handling
- Whitespace control
- Multiline slice
- Block errors
- Map filter with structs
- And more

Also added steve-ky as contributor for ideas/feedback on PR #89.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Test User

CHANGELOG.md

@@ -9,12 +9,58 @@
 
 - **Auto-Escape Feature** (#111): Implemented automatic HTML escaping for template output with opt-in/opt-out support via the `safe` filter. Output is automatically escaped by default when auto-escape is enabled, and can be marked as safe using `{{ value | safe }}`. Thanks [@dop251](https://github.com/dop251)
 
+- **Template Loader** (#107): Implemented custom template loader interface for flexible template storage. Thanks [@chrisatbd](https://github.com/chrisatbd)
+
+- **BasicEngine** (#104): Added `NewBasicEngine()` function for simpler engine instantiation without standard tags/filters. Thanks [@jam3sn](https://github.com/jam3sn)
+
+- **JSON Filter** (#84): Added `json` filter for JSON encoding. Thanks [@prestonprice57](https://github.com/prestonprice57)
+
+- **Strict Variables Mode** (#74): Added support for strict variable checking to catch undefined variables. Thanks [@jamesog](https://github.com/jamesog)
+
+- **Custom Writer Support** (#86): Added `FRender` to allow rendering into a custom `io.Writer`. Thanks [@jamslinger](https://github.com/jamslinger)
+
+- **Template AST Access** (#59, #66): Exposed template AST and lexical environment for introspection. Thanks [@carolynvs](https://github.com/carolynvs), [@aisbergg](https://github.com/aisbergg)
+
+- **For-Else Support** (#93): Implemented `else` clauses in `for` loops. Thanks [@codykrieger](https://github.com/codykrieger)
+
+- **Unless-Else Support** (#68): Allow `unless` tags to have `else` clauses. Thanks [@aisbergg](https://github.com/aisbergg)
+
+- **General Range Expressions** (#65): Allow range expressions as general expressions, not only in loops. Thanks [@aisbergg](https://github.com/aisbergg)
+
+- **Loop Modifier Expressions** (#67): Allow loop modifiers to be general expressions, not just literals. Thanks [@aisbergg](https://github.com/aisbergg)
+
 ### Changed
 
 - **Modernized Build Tooling** (#115): Updated golangci-lint configuration to v2 format, reorganized Makefile with comprehensive targets, and added pre-commit hooks for automated code quality checks. All existing lint and format issues have been resolved.
 
+- **Modernization** (#95): Various modernization improvements. Thanks [@danog](https://github.com/danog)
+
+- **GitHub Actions** (#87): Bumped GitHub workflow actions to latest versions. Thanks [@deining](https://github.com/deining)
+
 ### Fixed
 
+- **Size Filter** (#101): Count number of characters instead of bytes. Thanks [@jamslinger](https://github.com/jamslinger)
+
+- **Slice Bounds** (#99): Don't panic when slicing with index out of bound. Thanks [@jamslinger](https://github.com/jamslinger)
+
+- **Division by Zero** (#97): Don't panic in `divided_by` filter on division by zero. Thanks [@jamslinger](https://github.com/jamslinger)
+
+- **Nil Pointer** (#94): Fix panic in `ValueOf` with nil pointer. Thanks [@stephanejais](https://github.com/stephanejais)
+
+- **Nil Check** (#91): Add nil check for grammar field before `BlockSyntax` call. Thanks [@magiusdarrigo](https://github.com/magiusdarrigo)
+
+- **Whitespace Control** (#88, #78): Fix whitespace control and trimming. Thanks [@jamslinger](https://github.com/jamslinger), [@chrisghill](https://github.com/chrisghill), [@danog](https://github.com/danog)
+
+- **Multiline Slice** (#82): Fix slice on multiline strings. Thanks [@danog](https://github.com/danog)
+
+- **Block Errors** (#81): Bug fixes for `WrapError()`, `Errorf()` and `SourceFile()` in block context. Thanks [@wttw](https://github.com/wttw)
+
+- **Map Filter** (#71): Fix map filter with slice of structs. Thanks [@ofavre](https://github.com/ofavre)
+
+- **Documentation** (#69): Fix example filter URL in documentation. Thanks [@peteraba](https://github.com/peteraba)
+
+- **Windows Tests** (#61): Fixed include tag test cases on Windows
+
 - Fixed trailing whitespace issues in test files
 - Resolved all golangci-lint v2 compatibility issues