Fix #33: Libchula buffer escape issues

https://github.com/alobbs/libhpack/issues/33

There were three of Chula's buffer class related QA tests that were
failing.

The issues were origitaded from the right shifting operations inside the
*escape_with_table* fucntion.
Since there is no unsigned right shifting in C and we were working with
signed chars there were potential issues with values ranging from -127
to 0.
In all these cases the issue was with value 0xFF.

To solve this chars were changed to unsigned chars.
It probably was enough changing *s, but I preferred alos changing t,
s_next and end.

The tests that were failing were:

```
buffer_test.c:1127:F:escape_uri:escape_uri:0: Assertion 'b.buf=="%010.0000000.0000000.000000f"' failed: b.buf=="%00%01%1f%7f?", "%010.0000000.0000000.000000f"=="%00%01%1f%7f%ff"
```

```
buffer_test.c:1148:F:escape_uri_delims:escape_uri_delims:0: Assertion 'b.buf=="hola                   %00%1f                   %3a0.000000                      %5b2170432                                       %200.0000000.000000f   0x1.4c8e1a8p-1044dios!<>{}-_"' failed: b.buf=="hola%20%00%01%1f%20%3a%3f%23%5b%5d%40%20%7f%ff%20adios!<>{}-_", "hola                   %00%1f                   %3a0.000000                      %5b    0                                       %200.0000000.000000f           0x1p-1062dios!<>{}-_"==|"
```

```
buffer_test.c:1169:F:escape_arg:escape_arg:0: Assertion 'b.buf=="hola                   %00%1f                   %23                        %26 b0.000000                   %7f0.000000f   0x1.4c8deb8p-1044dios!@[]<>"' failed: b.buf=="hola%20%00%01%1f%20%23%25%26%2b%3f%20%7f%?f%20adios!@[]<>", "hola                   %00%1f                   %23                        %26 b0.000000                   %7f0.000000f  0x1.4c85d294p-1044dios!@[]<>"=="hola%20%00%01%1f%20%23%25%26%2b%3f%20%7f%ff%20adios!@[]<>"
```
Clean up

Removes a couple of unused files
Adds endianness detection
Adds SHA512 support
Adds new method

Implements a new hpack_header_block_clean() method
Merge pull request #34 from Akrog/issue33_chula

Fix #33: Libchula buffer escape issues
Fix #35: Libchula's *buf* should be unsigned

https://github.com/alobbs/libhpack/issues/35

After dettecting in issue 33 that having *chula_buffe_t -> buf* as
*char* created issues with bitwise operations, it was decided that:
>chula_buffe_t -> buf should be either uint8_t or unsigned char.
>The current signed type is somehow error prone for most common cases
>of the class.

This commit changes to *uint8_t* chula's *buf* field and also adds all
necessary casts in functions.

Also in file *buffer.c*, function *chula_buffer_cmp_buf* a *strncmp*
has been changed to a *memcmp*

Original: `return strncmp (A->buf, B->buf, B->len);`
Now: `return memcmp (A->buf, B->buf, B->len);`
Adds a new get_size() method

Implements a new hpack_header_field_get_size() method to the Header
Field class.
Merge pull request #36 from Akrog/issue#35

Fix #35: Libchula's *buf* should be unsigned
Fixes a few compilation warnings
"set -e" like behaviour during compilation
Do fail if any of the commands fail
Unifies the compiler flags
Merge branch 'gnu-sources'
Merge branch 'travisci-no-fail'
_FILE_OFFSET_BITS=64 support added
Fixes a few compilation warnings
Fixes quite a few compilation warnings

Most of the compilation warnings this patch fixes are related to the
types of the strings being compared.
Fixes compilation
CMake code to detect strerror_r()