This fixes a plethora of "not indexed" errors when the document has not been indexed.
* Message handler throws NotIndexed
* The message is put into backlog and tagged with backlog_path
* path2backlog keeps backlog associated with a document and a merged index clears the backlog
* backlog[0] is forced to run if it becomes overdue
* WorkingFiles::files : vector -> unordered_map
* Add timestamp to WorkingFile
* Rename "comp-preload" thread to "preamble"
* Rename CompletionManager to SemaManager as it is used by "diag" "comp" "preamble"
* Rename clang_complete.* to sema_manager.*
* Merge SemaManager::{preloads,sessions}
* Add initialization option session.maxNum
* In DiagnosticMain, if an included file was modified, cancel the DiagTask and create a PreambleTask instead. The task sets `from_diag` so as to trigger immediate DiagTask after the preamble is built.
Delete method.{cc,h}
Rename $ccls/setSkippedRanges to $ccls/publishSkippedRanges
Rename $ccls/publishSemanticHighlighting to $ccls/publishSemanticHighlight; stableId -> id
* Better LanguageId detection with clangDriver (e.g. .cu -> types::TY_CUDA)
* fallback when there is no .ccls or compile_commands.json
Also Hide clangTooling options from --help
