ShExC [1] is one syntax for the ShEx (shape expressions) language [2] to
describe the structure of RDF graphs (the other two syntaxes are based on
JSON-LD and RDF and don?t need special lexers). It is syntactically similar to
SPARQL, which is why a lot of the productions of ShExCLexer are copied from
SparqlLexer, but at the same time has enough differences that I feel it?s
better to simply copy the productions rather than trying to share them between
the two lexers (compare e.?g. PN_LOCAL_ESCAPE_CHARS or IRIREF).

The example file purports to be a brief schema for Pygments lexers, which I put
together from scratch to avoid licensing issues with existing example schemas;
it should not be taken too seriously.

[1]: https://shex.io/shex-semantics/#shexc
[2]: https://shexspec.github.io/primer/

Added lexer for Zig programming language

Add support for @import keyword in Objective-C

Directives were parsed independent of whitespace after them, which caused the
cpuid instruction to be parsed as CPU & id, instead of cpuid. We now expect a
whitespace character after a directive, which seems to match the Nasm
documentation.

In eea5abc9161a, we changed the TerminalFormatter to use bright instead of bold,
and this caused the tests here to fail.

Recognize single > as a prompt in doscon

fixes #1506