Prepare period documentation and improve static dependencies.

Makefile

@@ -65,7 +65,7 @@ imports: $(BBSTOOL-DEPS)
 bbstool: $(BBSTOOL-DEPS)
 	$(CSC) -o $@ $<
 
-bbstool-static: $(BBSTOOL-SOURCES)
+bbstool-static: $(BBSTOOL-DEPS)
 	$(CSC) -static -o $@ $(BBSTOOL-SOURCES)
 
 .PHONY: clean

README.md

@@ -191,6 +191,21 @@ Returns a new valid month that comes ```n``` months after ```m```. If
 
 ### Period
 
+This module implements simple calendar period handling with month
+granularity.
+
+sort-period-markers
+
+period-markers->periods
+
+periods-duration
+
+month-in-periods?
+
+periods->string
+
+periods-match
+
 ### Primes
 
 Generic Support Modules

period.scm

@@ -30,11 +30,8 @@
  (
   sort-period-markers
   period-markers->periods
-  period->duration
   periods-duration
-  month-in-period?
   month-in-periods?
-  period->string
   periods->string
   periods-match
   period-tests!