ref: Cleanup and rearrange files, update documentation

- Remove Ruby files since they aren't supported anymore
- Remove test and samples files
- Move all the "stable" plugins to `src` folder to follow standard conventions
- Update links and descriptions in the documentation

src/c/pid/Makefile

@@ -0,0 +1,18 @@
+UNAME_S := $(shell uname -s)
+ifeq ($(UNAME_S),Darwin)
+    LINK_FLAGS := -fno-common -flat_namespace -bundle -undefined suppress
+else
+    LINK_FLAGS := -shared -fpic
+endif
+
+all: pid.so
+
+%.so:%.o
+	$(CC) $(LINK_FLAGS) -lprofanity -o $@ $^
+
+%.o:%.c
+	$(CC) $(INCLUDE) -D_GNU_SOURCE -D_BSD_SOURCE -fpic -g3 -O0 -std=c99 \
+        -Wextra -pedantic -c -o $@ $<
+
+clean:
+	$(RM) pid.so