Codec `utf-16` aliases do not work in read_csv with c engine
#### Code Sample, a copy-pastable example if possible

```
import pandas

path = "test.csv"
pandas.DataFrame({"A": [0,1], "B": [2,3]}).to_csv(
    path, encoding="utf-16")

for encoding in ["utf-16","utf_16","UTF_16","UTF-16"]:
    try:
        pandas.io.parsers.read_csv(
            path,
            engine='c',
            encoding=encoding)
        print(encoding, "succeeded in c-pandas")
    except UnicodeDecodeError:
        print(encoding, "failed in c-pandas")

    try:
        pandas.io.parsers.read_csv(
            path,
            engine='python',
            encoding=encoding)
        print(encoding, "succeeded in pandas")
    except UnicodeDecodeError:
        print(encoding, "failed in pandas")

    try:
        with open(path, encoding=encoding) as file:
            file.read()
        print(encoding, "succeeded in open")
    except UnicodeDecodeError:
        print(encoding, "failed in open")
```
#### Expected Output

```
utf-16 succeeded in c-pandas
utf-16 succeeded in pandas
utf-16 succeeded in open
utf_16 succeeded in c-pandas
utf_16 succeeded in pandas
utf_16 succeeded in open
UTF_16 succeeded in c-pandas
UTF_16 succeeded in pandas
UTF_16 succeeded in open
UTF-16 succeeded in c-pandas
UTF-16 succeeded in pandas
UTF-16 succeeded in open
```
#### Actual Output

```
utf-16 succeeded in c-pandas
utf-16 succeeded in pandas
utf-16 succeeded in open
utf_16 failed in c-pandas
utf_16 succeeded in pandas
utf_16 succeeded in open
UTF_16 failed in c-pandas
UTF_16 succeeded in pandas
UTF_16 succeeded in open
UTF-16 failed in c-pandas
UTF-16 succeeded in pandas
UTF-16 succeeded in open
```
#### output of `pd.show_versions()`
## INSTALLED VERSIONS

commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Linux
OS-release: 4.6.2-1-ARCH
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8

pandas: 0.18.1
nose: 1.3.7
pip: 8.1.1
setuptools: 23.0.0
Cython: None
numpy: 1.11.0
scipy: 0.17.1
statsmodels: None
xarray: None
IPython: 4.2.0
sphinx: None
patsy: None
dateutil: 2.4.2
pytz: 2016.4
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.4.1
html5lib: None
httplib2: 0.9.2
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
pandas_datareader: None
