improve documentation

.clang-format

@@ -1,5 +1,6 @@
 ---
 BasedOnStyle: LLVM
+AccessModifierOffset: 0
 AllowShortBlocksOnASingleLine: false
 AllowShortFunctionsOnASingleLine: None
 AllowShortIfStatementsOnASingleLine: true

CONTRIBUTING.md

@@ -0,0 +1,33 @@
+# Contributing to xlnt
+
+xlnt welcomes contributions from everyone regardless of skill level (provided you can write C++).
+
+## Getting Started
+
+Look through the list of issues to find something interesting to work on. The issue description and labels should indicate the difficulty of implementation.
+
+## Contributions
+
+Contributions to xlnt should be made in the form of pull requests on GitHub. Each pull request will be reviewed and either merged into the master branch or given feedback for changes that would be required to do so. 
+
+All code in this repository is under the MIT License. You should agree to these terms before submitting any code to xlnt.
+
+## Pull Request Checklist
+
+- Branch from the master branch.
+
+- Commits should be as small as possible, while ensuring that each commit is correct independently (i.e. each commit should compile and pass all tests). Commits that don't follow the coding style indicated in .clang-format (e.g. indentation) cannot be accepted.
+
+- If your pull request is not getting reviewed or you need a specific person to review it, you can @-reply a reviewer asking for a review in the pull request or a
+  comment.
+
+- Add tests relevant to the fixed defect or new feature. It's best to do this before making any changes, make sure that the tests fail, then make changes ensuring that it ultimately passes the tests.
+
+## Conduct
+
+Just try to be nice--we're all volunteers here.
+
+
+## Communication
+
+Add a comment to an existing issue on GitHub, open a new issue for defects or feature requests, or contact @tfussell if you want.

TODO.md

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-For release:
-Move all method definitions out of headers.
-Clean up iterators in workbook, worksheet, cell_vector, range.
-One class per header.
-Set up Coveralls.
-Synchronize tests for workbook, worksheet, cell, core_properties, manifest, relationship, stylesheet, number_format, format_rule, tokenizer.
-Synchronize samples.
-Summarize what works and what doesn't.
-Finish documenting all header files.
-Port benchmarks.
-Clean up CMake scripts.
-Release 0.9.0 for Windows (static 32-bit, dll 32-bit, static 64-bit, dll 32-bit), Ubuntu 14.04 64-bit (static, shared), OSX 10.11 (static, dylib, framework).
-XML wrappers aren't very pretty, improve them?
-100% test coverage.
-
-Then:
-Implement conditional formatting.
-Implement charts.
-Implement chartsheets.
-Implement drawing.
-Implement formula evaluation?
-Implement pivot tables.
-Implement XML validation.