ccstreams - Custom C Streams

CCStreams is a collection of custom C IO streams (FILE *). They can generally
be used in the same way as any FILE stream pointer (fread, fwrite, fprintf,
etc). Some specialization is done depending on the specific backing store for
the stream. For example, the string stream has the unique ability of being
truncatable by writing a NULL byte to it. The guiding principle is to provide
streams (as if they were created from a file on disk) that behave in the least
surprising way for a given backing store.

Types of streams:

* str - A C string (NULL-terminated character array).
* mem - A dynamically allocated memory buffer.

See test/example/*.c for example programs using these streams.

Motivation

Some of you may be wondering why fmemopen and open_memstream weren't
sufficient. Initially I considered using open_memstream, but it doesn't permit
reuse of an existing buffer. fmemopen does, but it won't dynamically allocate
the buffer if it needs to grow. Basically, I needed something that was both
fmemopen AND open_memstream (and some additional niceties like a truncatable
string stream). Unfortunately no such stream existed and so ccstreams_fstropen
was born.

The memory buffer stream was just a logical extension of the symantics of the
C string stream. It lacks the ability to be truncated, but it can contain any
kind of data. Like the C string stream, it can reuse existing data in the
buffer (which can't be done with open_memstream).

IMO, these streams behave more like typical file streams than those provided
by fmemopen and open_memstream. They adhere to the meaning of the mode
parameter as per fopen(...). They grow in size as a file would. You can't seek
past the end of the stream. Etcetera.