docs: fix up some comp docs that had rotted a bit

The docs referred to an old name of an internal data structure.  The code
changed in a7a7fd3 but i forgot to update the docs.

The new name includes the underscore character "_", which is meaningful
to asciidoc.  This commit changes the markup delineating the name from
single-tick "'" to backtick "`", to tell asciidoc to pass through the
text without further substitution.  This also changes the rendering
from italic to monospace, which is arguably better anyway (though it's
somewhat inconsistent with the surrounding markup).

This commit also fixes a markup syntax blooper in the FOR_ALL_INSTS()
documentation.

docs/src/hal/comp.txt

@@ -355,10 +355,10 @@ problems include:
 == Convenience Macros
 
 Based on the items in the declaration section, 'comp' creates a C
-structure called 'struct state'. However, instead of referring to the
-members of this structure (e.g., '*(inst->name)' ), they will generally
+structure called `struct __comp_state`. However, instead of referring to the
+members of this structure (e.g., `*(inst->name)`), they will generally
 be referred to using the macros below. The 
-details of 'struct state' and these macros may change from one version
+details of `struct __comp_state` and these macros may change from one version
 of 'comp' to the next.
 
 * 'FUNCTION(name)' - Use this macro to begin the definition of a realtime function which
@@ -399,8 +399,8 @@ When the item is a conditional item, it is only legal to refer to it
 * 'fperiod' - The floating-point number of seconds between calls to this realtime
     function.
 
-* 'FOR_ALL_INSTS() {...}' - For userspace components. This macro uses the variable 'struct
-    state 'inst' to iterate over all the defined instances. Inside the
+* 'FOR_ALL_INSTS() {...}' - For userspace components. This macro
+    iterates over all the defined instances. Inside the
     body of the 
      loop, the 'pin_name', 'parameter_name', and 'data' macros work as they
     do in realtime functions.