Allow chunking algorithm to be specified when adding a file

[dordille]

Adds functionality to enable rabin chunking as described by /issues/1283.

This mirrors the api defined by the go library, usage via command line as follows.

$ ./src/cli/bin.js add --chunker rabin-48-96-192 LICENSE
added QmZH1VRMjDD48A7uqzaEU6qdfk4ddNVKZLnBMN1Lc1iEic LICENSE
$ ./src/cli/bin.js object links QmZH1VRMjDD48A7uqzaEU6qdfk4ddNVKZLnBMN1Lc1iEic
QmamX3HDpMkE6NNun2pvz1UmBubA1nsuEzMEnBqUSVXy5E 180
QmdH3L1zu7hWu7nrpoCe33zfn3hDm6baYpTSENbRitpcFu 140
Qmaw7roFAKSj3V3QxmFUfpqU3dqAEMPMqHynqXxJmhhGhB 64
Qmewm77gB4V7cgnZLsuikXgrG8Q38M1TX8qPRBcKrw4yJ4 90
QmRd6EoLAyp6TXZmSRTByaAgEn5632J8u9NwFSiHfXurLx 95
QmeLhozoTP1z3RiLRBRUuLJ7xpmDh5oi1ShN91B4UPjRwA 172
QmdxhoXpK74gGbm2G8bAoCiuqDfbq44rN6RZKefCAFEhoZ 99
QmZNEhqU6uVjMc7p7xfqfwQK5YGxe1bdUNdG6Hq81149iw 139
Qmd1yFj2ZuNd28r5MaQaWkr3vcUwPF61i8oBdfRjaUC4V5 64
QmeJhcwipWbjXA5DdXVGe6Sh8kwBzADNnw3Zd3HKcPtPkm 82
Qme1G8Mk1PLThzCr11NzChQVy1FJoHCQkjK7rB2iTWKkaJ 58

[dordille]

Closing in favor of #1469 with proper commit message formatting.