readme: move release history to HISTORY.md and roadmap to ROADMAP.md

Former-commit-id: e37e422

Author: mewmew

HISTORY.md

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+# Release history
+
+## Version 0.3 (to be released)
+
+Primary focus of version 0.3: *grammar covering the entire LLVM IR language*.
+
+The grammar for LLVM IR is now complete and covers the entire LLVM IR language (as of LLVM 7.0).
+
+Lexers and parsers for LLVM IR assembly are automatically generated from a [EBNF grammar](https://github.com/llir/grammar/blob/master/ll.tm) using [Textmapper](https://github.com/inspirer/textmapper).
+
+The Textmapper generated source code has been split into a [dedicated repository](https://github.com/llir/ll).
+
+## Version 0.2 (2017-06-24)
+
+Primary focus of version 0.2: *read and write support of LLVM IR assembly*.
+
+Lexers and parsers for LLVM IR assembly are automatically generated from a [BNF grammar](https://github.com/llir/llvm/blob/28149269dab73cc63915a9c2c6c7b25dbd4db027/asm/internal/ll.bnf) using [Gocc](https://github.com/goccmack/gocc).
+
+A high-level API for parsing LLVM IR assembly is provided by [llvm/asm](https://godoc.org/github.com/llir/llvm/asm).
+
+The [llvm/ir](https://godoc.org/github.com/llir/llvm/ir) package supports all instructions of LLVM IR, except the instructions used for concurrency and exception handling.
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+The llir/llvm packages are now go-getable, as the Gocc generated source code has been added to the source tree.
+
+## Version 0.1 (2015-04-19)
+
+Initial release.
+
+Preliminary work on the `llvm/ir` package which provides an in-memory representation of LLVM IR in pure Go.
+
+Hand-written lexer and preliminary work on a recursive descent parser for LLVM IR assembly.

ROADMAP.md

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+# Roadmap
+
+## Version 0.4 (to be released)
+
+Primary focus of version 0.4: *data flow analysis*.
+
+Introduce API for use-def chains.