Fix symbol list

[gwenzek]

• mark function calls as such
• make sure we have an index entry for enum, union Symbol detection gives incorrect locations #64
• usage of type isn't a type definition Symbol detection gives incorrect locations #64
• rename a few "storage.type" into "keyword.declaration" (for fn, test, ... )
• update readme to talk about the two different syntaxes

[TheGag96]

Just tried a few files. This works pretty well!!