Issue #26: New integer tests

https://github.com/alobbs/libhpack/issues/26

There were several important cases that were not tested by *integer_test.c*

Added tests:
- *decode_too_big_for_int*: Decodes a number > INT_MAX
- *decode_too_big_for_uint*: Tries to decode a number > UINT_MAX
- *decode_too_big_for_ulong*: Tries to decode a number > ULONG_MAX
- *en_decode_max_uint_5bits*: Encode/Decode INT_MAX with 5 bit prefix
- *en_decode_2nd_byte_0*: Encode a number with 1st byte 1s and 2nd 0s
- *decode_too_many_zeros*: Tries to decode a number with too many zeros

Most of these tests fail with the current integer encoding/decoding
algoritm.
Fix #26: New VLQ integer encoding/decoding

https://github.com/alobbs/libhpack/issues/26

Encoding would encode numbers greater than INT_MAX.
Now it can enconde up to UINT_MAX.

Decoding would have trouble with:
- Numbers greater than INT_MAX --> Return negative number
- Numbers greater than UINT_MAX
- Would process all bytes of a stream with many zeros

According to the draft if we encounter too big a number or too many
zeros in the encoding we should consider this an error. Now it does.
Fix #26: integer.h amends

https://github.com/alobbs/libhpack/issues/26

Changes to integer.h:
- Removed *MIN macro*
- Renamed *MAX_LEN_INTEGER* to *VLQ_MAX_LEN_INTEGER*
Fix #26: integer.c amends

https://github.com/alobbs/libhpack/issues/26

Changes to integer.c:
- Renamed *MAX_LEN_INTEGER* to *VLQ_MAX_LEN_INTEGER*
Merge pull request #28 from Akrog/integer_fix2

Issue #26: New integer tests

There were several important cases that were not tested by integer_test.c

Added tests:

decode_too_big_for_int: Decodes a number > INT_MAX
decode_too_big_for_uint: Tries to decode a number > UINT_MAX
decode_too_big_for_ulong: Tries to decode a number > ULONG_MAX
en_decode_max_uint_5bits: Encode/Decode INT_MAX with 5 bit prefix
en_decode_2nd_byte_0: Encode a number with 1st byte 1s and 2nd 0s
decode_too_many_zeros: Tries to decode a number with too many zeros
Most of these tests fail with the current integer encoding/decoding
algoritm.