Add support for all binary and hexadecimal literal syntaxes - #245

…tation (#255)

This fixes the following error:
```bash
SQLSTATE[HY000]: General error: 1 unrecognized token: "x'1'"
```

For queries like the following:
```sql
SELECT 0b1;
SELECT 0b01;
SELECT 0b001;
...
```

SQLite doesn't have binary string literals, so [we need to convert them
to HEX string
literals](#245).
However, HEX string literals in SQLite must be aligned to full bytes
(their length needs to be even) — `x'01'` is valid, while `x'1'` is
invalid.

In MySQL, binary strings don't require such alignment, and `0b1` is
valid (and `SELECT 0b1 = 0b01` returns `true`).

Additionally, the `base_convert()` function used in the [original
implementation](#245)
doesn't preserve existing leading `0` padding.

To solve both of these issues, this PR implements the following:
1. Count how many full bytes the original binary string requires.
2. Make sure the resulting HEX string has that number of bytes, using
leading `0` padding.

For HEX strings, this fix is not needed, as those require to be
byte-aligned also in MySQL, so throwing an error for `x'1'` is actually
correct.