Remove function 'normalize' in MAC address parsing

This function was used for the case that there was only one octet in a
MAC address fragment. Example:

f:f:f:3:3:3

This kind of addresses are not valid MAC addresses but libpcap accepts
them. When there's an address like this, what is missing is the leading
zero, not the trailing zero. The 'normalize' function considered
that the octet missing was the trailing zero, and wrongly shifted the
octet 4 bits.
Operators 'fddi', 'tr' and 'wlan' are aliases of 'ether'
Added tests for logical operator parsing
Simplify logical expression parsing

Since 'and' and 'or' have the same precedence, it is only important whether
'max_precedence' is infinity(default). Hence, it can be replaced with
a boolean flag.
Merge pull request #68 from Igalia/fix-ether-normalize

Remove function 'normalize' in MAC address parsing
Merge pull request #69 from Igalia/ether-alias

Operators 'fddi', 'tr' and 'wlan' are aliases of 'ether'
Implement lowering 'decnet'

Examples:

- decnet src [host] <decnet-address>.
- decnet dst [host] <decnet-address>.
- decnet host <decnet-address>.
Add examples 'decnet src 10.15' 'decnet host 10.15'
Merge pull request #67 from Igalia/low-decnet

Implement lowering 'decnet'
Add technical document explaining BPF asm code for different operators
Fix syntax error
Add example 'ip proto sctp'
Merge pull request #76 from Igalia/fix-doc-generation

Fix doc generation
Implement lowering of isis protocols
Add example 'l1'
Merge pull request #74 from Igalia/low-isis

Implement lowering of ISIS protocols
Merge pull request #75 from Igalia/tech-doc

Add technical document explaining BPF asm code for different operators
Merge pull request #78 from mpeterv/fix-logical-precedence

Fix parsing of logical expressions