wrapper.rb: properly calculate length of string in bytes.
Fixed bug in install target.
Added ast.[c,h] for AST definitions and AST-manipulating functions.
Rename cmark_free_nodes -> cmark_free_blocks.
Moved cmark_free_inlines from inlines to ast.
Added bench.h and inserted timing macros in main.

`make TIMER=1` to build with timings.
inline static -> static inline for consistency.
Moved the timing macros to get finer-grained information.
Make dingus.html valid HTML5
Fix some links in the README (stmd -> CommonMark for the Git repo)
Merge pull request #196 from Thiht/master

Minor modifications
bench.h - adjusted timing width.
Moved ast-manipulating functions from inlines to ast.
Moved scan_at out of scanners.h, renamed to _scan_at.
Compile with -fvisibility=hidden.

We'll mark public functions as "default".
Make basic functions in cmark.h visible.
Removed ast modules, moved these defs back to cmark.h.
Added cmark_append_blocks, exposed more functions.
Made buffer functions visible in shared library.
Use time.h, not sys/time.h.