Change latest released version to 0.7.1

Please was pushed to NuGet as version 0.7.0 but as soon as I tried to install version 0.7.0 I received an error because Please is setup as a tool in its NuGet package and therefore can't reference dependencies that target projects (Simpler and Castle.Core). The dependencies aren't needed anyway since ILMerge was used to combine everything into a single `please.exe`. The fix required a bump to 0.7.1 and another push to NuGet.

Note: There have been several PRs merged to master since 0.7.0 so the code that was used to build 0.7.0 and 0.7.1 came from [this commit](https://github.com/ResourceDataInc/please/commit/a25ec6dd41fb7d6590c573f73ee54935551c4288). 

This PR is related to #8.

Todo

- [ ] Change the CI scripts back to using ILMerge for releases post-0.7.1 (one of the PRs that has been merged to `master` removed it)