Fix typos in ARCHITECTURE.md and a number of crates

specifically: gen_lsp_server, ra_arena, ra_cli, ra_db, ra_hir

crates/ra_hir/src/lib.rs

@@ -1,9 +1,9 @@
-//! HIR (previsouly known as descriptors) provides a high-level OO acess to Rust
-//! code.
+//! HIR (previously known as descriptors) provides a high-level object oriented
+//! access to Rust code.
 //!
 //! The principal difference between HIR and syntax trees is that HIR is bound
 //! to a particular crate instance. That is, it has cfg flags and features
-//! applied. So, there relation between syntax and HIR is many-to-one.
+//! applied. So, the relation between syntax and HIR is many-to-one.
 
 macro_rules! ctry {
     ($expr:expr) => {