Added tonumber support #71

pkg/yqlib/doc/operators/headers/to_number.md

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+# To Number
+Parses the input as a number. yq will try to parse values as an int first, failing that it will try float. Values that already ints or floats will be left alone.

pkg/yqlib/doc/operators/to_number.md

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+# To Number
+Parses the input as a number. yq will try to parse values as an int first, failing that it will try float. Values that already ints or floats will be left alone.
+
+## Converts strings to numbers
+Given a sample.yml file of:
+```yaml
+- "3"
+- "3.1"
+- "-1e3"
+```
+then
+```bash
+yq '.[] | to_number' sample.yml
+```
+will output
+```yaml
+3
+3.1
+-1e3
+```
+
+## Doesn't change numbers
+Given a sample.yml file of:
+```yaml
+- 3
+- 3.1
+- -1e3
+```
+then
+```bash
+yq '.[] | to_number' sample.yml
+```
+will output
+```yaml
+3
+3.1
+-1e3
+```
+
+## Cannot convert null
+Running
+```bash
+yq --null-input '.a.b | to_number'
+```
+will output
+```bash
+Error: cannot convert node value [null] at path a.b of tag !!null to number
+```
+