Allow reading field lists with packed types (#30)

Field lists were parsed correctly for value types (e.g. `(field i32)`),
but not for packed types (e.g. `(field i8)`)

Add build instructions to README.md (#26)

Implement ToText, for converting binary -> text (#21)

Add support for Win32 (#11)

* Fix circleci build
* Add github actions build
* Split CMakeLists.txt into separate subdirectories
* Remove declaration of std::hash, using <functional> header
* Add operator{==,!=} for comparing At<T> with T
* Fix infinite loop in WriteVarIntLoop (cast to u8)
* Use data accessor instead of begin()/end() to get char*
* Some integer cast fixes
* Add text::Write{Nat,Int,Float}, to fix overloading issues
* Use CTest for running each unittest executable
* Only include -lstdc++fs if necessary
* Copy gdtoa library into source tree; modify to compile w/ MSVC
* Fix warning when using -2147483648 literal
* Use gtest_force_shared_crt to prevent CRT mismatch