Windows support: portable local server launch + clean quit, %APPDATA% data dir, Win32 libs, MinGW/MSVC build docs

shared/Protocol.h

@@ -75,7 +75,10 @@ enum class ActionKind : uint8_t {
 
 class Writer {
 public:
-    explicit Writer(Msg m) { u8(uint8_t(m)); }
+    explicit Writer(Msg m) {
+        buf_.reserve(64);  // most messages fit; avoids regrowth for every field
+        u8(uint8_t(m));
+    }
     void u8(uint8_t v) { buf_.push_back(v); }
     void u16(uint16_t v) { raw(&v, 2); }
     void u32(uint32_t v) { raw(&v, 4); }