Created version.h markdown.

doc/api/mruby/version.h.md

+#### Macros
+### MRUBY_RUBY_VERSION
+The version of Ruby used by mruby.
+### MRUBY_RUBY_ENGINE
+Ruby engine.
+### MRUBY_VERSION
+The mruby version.
+### MRUBY_RELEASE_MAJOR
+Major release version.
+### MRUBY_RELEASE_MINOR
+Minor release version.
+### MRUBY_RELEASE_NO
+Release number.
+### MRUBY_RELEASE_DATE
+Release date as a string.
+### MRUBY_RELEASE_YEAR
+Release year.
+### MRUBY_RELEASE_MONTH
+Release month.
+### MRUBY_RELEASE_DAY
+Release day.
+### MRUBY_BIRTH_YEAR
+The year mruby was first created.
+### MRUBY_AUTHOR
+Mruby's authors.
+### MRB_STRINGIZE0(expr)
+A passed in expression.
+### MRB_STRINGIZE(expr)
+Passes in an expression to MRB_STRINGIZE0.
+### MRUBY_DESCRIPTION
+mruby's version, and release date.
+### MRUBY_COPYRIGHT
+mruby's copyright information.