Extensions and changes from LANL

[The following is the contents of README_0.5.2 ...]

This is not (yet) an officially-released version of aws4c.  0.5.2
represents unofficial extensions to the 0.5 release, by Los Alamos National
Laboratory.

We attempted to preserve functionality of all interfaces provided by 0.5.
Where new functionality was added, we've typically added new interfaces.

(1) Extensions to IOBuf / IOBufNode.

The 0.5 version simply adds strings into a linked list, via a malloc and
strcpy().  This might be acceptable when all that's needed is to parse
individual response headers, but we wanted to support more-efficient
operations when large buffers are being sent or received.  Thus, it is now
possible to add data for writing by installing user buffers directly into
an IOBuf's linked list.  It is also possible to add storage for receiving
data in a similar way.  In either case, the added storage may be static or
dynamic.  Here are some typical scenarios.

    // GET an object from the server into user's <data_ptr>
    //     NOTE: this uses the "extend" functions to add unused storage
    aws_iobuf_reset(io_buf);
    aws_iobuf_extend_static(io_buf, data_ptr, data_length);
    AWS4C_CHECK( s3_get(io_buf, obj_name) );
    AWS4C_CHECK_OK( io_buf );

    // PUT the contents of user's <data_ptr>
    //     NOTE: this uses the "append" functions to add data
    aws_iobuf_reset(io_buf);
    aws_iobuf_append_static(io_buf, data_ptr, data_length);
    AWS4C_CHECK( s3_put(io_buf, obj_name) );
    AWS4C_CHECK_OK( io_buf );

These use cases will typically also want to call aws_iobuf_reset() after
completion, so as to avoid keeping a pointer internal to the IOBuf which
will go out of scope.

(2) Re-using connections

In 0.5, every call to aws4c functions creates a new CURL connection.  This
can add overhead to an application that is performing many operations.  We
allow the user to specify that connections should be preserved, or to reset
the connection at a specific time.

    aws_reuse_connections(1); // begin reusing connections
    // ...
    aws_reset_connection();   // reset the connection once
    // ...
    aws_reuse_connections(0); // stop reusing connections

(3) GET/PUT to/from file

Companion-functions to the 0.5 head/get/put/post functions allow user to
specify a file.  This also allows user to provide one IOBuf to capture the
response, in addition to one used to send the request.

(4) binary data

The old getline() function was not very useful for reading arbitrary
streams of binary (or text data).  We added a get_raw() function that
ignores newlines.

(5) EMC extensions

EMC supports some extensions to "pure" S3, such as using byte-ranges to
write parts of an object in parallel, or to append to an object.  These
normally aren't legal, so you have to call a special function to allow the
library support to be used:

    // use byte-range to append to an object
    s3_enable_EMC_extensions(1);
    s3_set_byte_range(-1, -1);   // creates "Range: bytes=-1-"
    s3_put(io_buf, obj_name);

    // another interface to append to an object
    s3_enable_EMC_extensions(1);
    emc_put_append(io_buf, obj_name);

    // instead of multi-part upload ...
    s3_enable_EMC_extensions(1);
    s3_set_byte_range(offset, length);
    s3_put(io_buf, obj_name);

(6) extras

The 0.5.2 makefile builds a library, libaws4c.  We also provide some
debugging functions and XML support, which probably should not be part of
the default library.  Therefore, these have their own header
(aws4c_extras.h) and are built into a separate library libaws4c_extras.
This allows test-apps to use extra functionality, without requiring the
production library to be as big.

(7) unit-tests

Feel free to add new unit-tests to test_aws.c This allows simple tests of
new functions, and provides a crude regression-test.