Update n3.pest

For the tbox rule `{?X :src_advisor ?Y} => {?X :advisor ?Y}.`
we currently get
```
Loading data ABox and TBox
thread 'main' panicked at 'Unable to read: Error { variant: ParsingError { positives: [WS], negatives: [] }, location: Pos(161), line_col: Pos((5, 9)), path: None, line: "{?X :src_advisor ?Y} => {?X :advisor ?Y}.␊", continued_line: None }', lib/src/n3_parser.rs:44:71
```
Underscores are allowed in local name part of a qname and this PR is a quick hack to adsress that.

lib/src/parsing/n3.pest

@@ -75,7 +75,8 @@ NewLine = { "\r" | "\n" }
 Var = {"?"~ASCII_ALPHA+~ASCII_ALPHANUMERIC*}
 Prefix = {"@prefix"~SPACE+~PrefixIdentifier~":"~SPACE+~"<"~Iri~">"~WS* ~"."~WS*}
 PrefixIdentifier = {ASCII_ALPHANUMERIC*}
-Prefixed = {PrefixIdentifier ~":"~ASCII_ALPHANUMERIC+}
+LocalNameChar = {ASCII_ALPHANUMERIC | "_"}
+Prefixed = {PrefixIdentifier ~":"~LocalNameChar+}
 Term = {"<"~Iri~">" | Prefixed}
 varOrTerm = { Term | Var}
 Subject = { Term | Var}
@@ -85,4 +86,4 @@ TP = { WS*~Subject ~WS+~ Property ~WS+~ Object ~WS* ~"."? ~WS* }
 Body = {"{"~TP+~"}"}
 Head = {"{"~WS*~TP~WS*~"}"}
 rule = { Body~WS*~"=>"~WS*~Head~WS*~"."? ~WS*}
-document = {Prefix* ~ NewLine* ~rule+}
+document = {Prefix* ~ NewLine* ~rule+}