bloom: added (probably) usefull notes
stat: added notes about atomicity of update
index: allocate index blocks in contious region

This decreases allocator pressure on start and decreases memory
fragmentation.

This also stepping stone for removal of index blocks tree which will
further reduce memory footprint and possibly increase speed.
stress: missing whitespace in help
stress: change default sync to -1
cpp: add ability to read w/o checksumming

Added overloaded versions of following functions:
    std::string read(...)
    int read(...)
    void read_hashed(...)
    std::string read_hashed(...)

Now they accept parameter of type
    enum eblob_read_flavour csum
which can be either:
    EBLOB_READ_CSUM
    EBLOB_READ_NOCSUM