Return diagnostic data as object from JSON methods

[rturrado]

API methods returning a JSON now follow the Diagnostic structure of the Language Server Protocol (LSP) specification.

We've taken the opportunity to refactor the libqasm's "error handling". Every ParseResult and AnalysisResult manages a vector of Error objects, instead of a vector of strings. This way, the formatting of an error object is delayed right until the API implementation.

All the syntactic error messages start with Error: or Error at <location>:'. And many of them include a <last column> field. This change should fix issue #178.

Refactor error::AnalysisError:

• Rename it to Error, since this class is used both for parse and analysis errors.
• Add ParseError and AnalysisError aliases.
• Make the class copyable. Thus changing the unique pointer to location for a shared pointer.
• Add a constructor receiving a message and a source location. This is needed when building an error from the CustomErrorListener.
• Add to_json method, operator<<, and enable the class to be used via fmt. The JSON string follows the Language Server Protocol (LSP) specification. Every error is mapped to an LSP Diagnostic structure.
• Remove the ostringstream message member. I find that overcomplicates the class.
• Remove the get_message method. I find keeping the what method alone is enough.

Refactor annotations::SourceLocation:

• Enable the class to be used via fmt.

Refactor CustomErrorListener::syntaxError:

• Throw an error::ParseError instead of a std::runtime_error with a formatted message. This change should fix issue #178.

Refactor v1x::Analyzer:

• API is consistent with that of v3x. Change methods to non-const. Change analyze(const ParseResult &) to analyze(ParseResult &&). TODO: I am not very sure about this change. Yes, both v1x and v3x APIs are now consistent. But why remove constness from an API (which is a good thing)?

Update references to error::AnalysisError in the code.

• Use error::ParseError or error::AnalysisError depending on if the code is doing parsing or analysis.

Add .gitattributes file.

• To enforce LF line endings on resource files during checkout. This way, golden test files have LF line endings, and can be successfully compared to actual files, that are always written out with LF line endings. This change should fix issue #152.

Add cmake-build-* folders to .gitignore.

[rturrado]

Many thanks for the review, Pablo.

I may not have gone the whole way with the use of optional, but it has indeed made the API clearer now. I don't like at all default arguments.

Thanks for this kind of review suggestions.